libgo/go/runtime/iface.go - gofrontend - Git at Google

 // Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package runtime

 import (
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
 )

 // For gccgo, use go:linkname to export compiler-called functions.
 //
 //go:linkname requireitab
 //go:linkname assertitab
 //go:linkname panicdottype
 //go:linkname ifaceE2E2
 //go:linkname ifaceI2E2
 //go:linkname ifaceE2I2
 //go:linkname ifaceI2I2
 //go:linkname ifaceE2T2P
 //go:linkname ifaceI2T2P
 //go:linkname ifaceE2T2
 //go:linkname ifaceI2T2
 //go:linkname ifaceT2Ip
 // Temporary for C code to call:
 //go:linkname getitab

 // The gccgo itab structure is different than the gc one.
 //
 // Both gccgo and gc represent empty interfaces the same way:
 // a two field struct, where the first field points to a type descriptor
 // (a *_type) and the second field is the data pointer.
 //
 // Non-empty interfaces are also two-field structs, and the second
 // field is the data pointer. However, for gccgo, the first field, the
 // itab field, is different. The itab field points to the interface
 // method table, which is the implemention of a specific interface
 // type for a specific dynamic non-interface type.  An interface
 // method table is a list of pointer values. The first pointer is the
 // type descriptor (a *_type) for the dynamic type. The subsequent
 // pointers are pointers to function code, which implement the methods
 // required by the interface. The pointers are sorted by name.
 //
 // The method pointers in the itab are C function pointers, not Go
 // function pointers; they may be called directly, and they have no
 // closures. The receiver is always passed as a pointer, and it is
 // always the same pointer stored in the interface value. A value
 // method starts by copying the receiver value out of the pointer into
 // a local variable.
 //
 // A method call on an interface value is by definition calling a
 // method at a known index m in the list of methods. Given a non-empty
 // interface value i, the call i.m(args) looks like
 //     i.itab[m+1](i.iface, args)

 // Both an empty interface and a non-empty interface have a data
 // pointer field. The meaning of this field is determined by the
 // kindDirectIface bit in the `kind` field of the type descriptor of
 // the value stored in the interface. If kindDirectIface is set, then
 // the data pointer field in the interface value is exactly the value
 // stored in the interface. Otherwise, the data pointer field is a
 // pointer to memory that holds the value. It follows from this that
 // kindDirectIface can only be set for a type whose representation is
 // simply a pointer. In the current gccgo implementation, this is set
 // for types that are pointer-shaped, including unsafe.Pointer, channels,
 // maps, functions, single-field structs and single-element arrays whose
 // single field is simply a pointer-shaped type.

 // For a nil interface value both fields in the interface struct are nil.

 // itabs are statically allocated or persistently allocated. They are
 // never freed. For itabs allocated at run time, they are cached in
 // itabTable, so we reuse the same itab for the same (interface, concrete)
 // type pair. The gc runtime prepopulates the cache with statically
 // allocated itabs. Currently we don't do that as we don't have a way to
 // find all the statically allocated itabs.

 const itabInitSize = 512

 var (
 	itabLock      mutex                               // lock for accessing itab table
 	itabTable     = &itabTableInit                    // pointer to current table
 	itabTableInit = itabTableType{size: itabInitSize} // starter table
 )

 // Cache entry type of itab table.
 // For gccgo, this is not the data type we used in the interface header.
 type itab struct {
 	inter   *interfacetype
 	methods [2]unsafe.Pointer // method table. variable sized. first entry is the type descriptor.
 }

 func (m *itab) _type() *_type {
 	return (*_type)(m.methods[0])
 }

 // Note: change the formula in the mallocgc call in itabAdd if you change these fields.
 type itabTableType struct {
 	size    uintptr             // length of entries array. Always a power of 2.
 	count   uintptr             // current number of filled entries.
 	entries [itabInitSize]*itab // really [size] large
 }

 func itabHashFunc(inter *interfacetype, typ *_type) uintptr {
 	// compiler has provided some good hash codes for us.
 	return uintptr(inter.typ.hash ^ typ.hash)
 }

 // find finds the given interface/type pair in t.
 // Returns nil if the given interface/type pair isn't present.
 func (t *itabTableType) find(inter *interfacetype, typ *_type) *itab {
 	// Implemented using quadratic probing.
 	// Probe sequence is h(i) = h0 + i*(i+1)/2 mod 2^k.
 	// We're guaranteed to hit all table entries using this probe sequence.
 	mask := t.size - 1
 	h := itabHashFunc(inter, typ) & mask
 	for i := uintptr(1); ; i++ {
 		p := (**itab)(add(unsafe.Pointer(&t.entries), h*sys.PtrSize))
 		// Use atomic read here so if we see m != nil, we also see
 		// the initializations of the fields of m.
 		// m := *p
 		m := (*itab)(atomic.Loadp(unsafe.Pointer(p)))
 		if m == nil {
 			return nil
 		}
 		if m.inter == inter && m._type() == typ {
 			return m
 		}
 		h += i
 		h &= mask
 	}
 }

 // itabAdd adds the given itab to the itab hash table.
 // itabLock must be held.
 func itabAdd(m *itab) {
 	// Bugs can lead to calling this while mallocing is set,
 	// typically because this is called while panicing.
 	// Crash reliably, rather than only when we need to grow
 	// the hash table.
 	if getg().m.mallocing != 0 {
 		throw("malloc deadlock")
 	}

 	t := itabTable
 	if t.count >= 3*(t.size/4) { // 75% load factor
 		// Grow hash table.
 		// t2 = new(itabTableType) + some additional entries
 		// We lie and tell malloc we want pointer-free memory because
 		// all the pointed-to values are not in the heap.
 		t2 := (*itabTableType)(mallocgc((2+2*t.size)*sys.PtrSize, nil, true))
 		t2.size = t.size * 2

 		// Copy over entries.
 		// Note: while copying, other threads may look for an itab and
 		// fail to find it. That's ok, they will then try to get the itab lock
 		// and as a consequence wait until this copying is complete.
 		iterate_itabs(t2.add)
 		if t2.count != t.count {
 			throw("mismatched count during itab table copy")
 		}
 		// Publish new hash table. Use an atomic write: see comment in getitab.
 		atomicstorep(unsafe.Pointer(&itabTable), unsafe.Pointer(t2))
 		// Adopt the new table as our own.
 		t = itabTable
 		// Note: the old table can be GC'ed here.
 	}
 	t.add(m)
 }

 // add adds the given itab to itab table t.
 // itabLock must be held.
 func (t *itabTableType) add(m *itab) {
 	// See comment in find about the probe sequence.
 	// Insert new itab in the first empty spot in the probe sequence.
 	mask := t.size - 1
 	h := itabHashFunc(m.inter, m._type()) & mask
 	for i := uintptr(1); ; i++ {
 		p := (**itab)(add(unsafe.Pointer(&t.entries), h*sys.PtrSize))
 		m2 := *p
 		if m2 == m {
 			// A given itab may be used in more than one module
 			// and thanks to the way global symbol resolution works, the
 			// pointed-to itab may already have been inserted into the
 			// global 'hash'.
 			return
 		}
 		if m2 == nil {
 			// Use atomic write here so if a reader sees m, it also
 			// sees the correctly initialized fields of m.
 			// NoWB is ok because m is not in heap memory.
 			// *p = m
 			atomic.StorepNoWB(unsafe.Pointer(p), unsafe.Pointer(m))
 			t.count++
 			return
 		}
 		h += i
 		h &= mask
 	}
 }

 // init fills in the m.methods array with all the code pointers for
 // the m.inter/m._type pair. If the type does not implement the interface,
 // it sets m.methods[1] to nil and returns the name of an interface function that is missing.
 // It is ok to call this multiple times on the same m, even concurrently.
 func (m *itab) init() string {
 	inter := m.inter
 	typ := m._type()
 	ni := len(inter.methods) + 1
 	methods := (*[1 << 16]unsafe.Pointer)(unsafe.Pointer(&m.methods[0]))[:ni:ni]
 	var m1 unsafe.Pointer

 	ri := 0
 	for li := range inter.methods {
 		lhsMethod := &inter.methods[li]
 		var rhsMethod *method

 		for {
 			if ri >= len(typ.methods) {
 				m.methods[1] = nil
 				return *lhsMethod.name
 			}

 			rhsMethod = &typ.methods[ri]
 			if (lhsMethod.name == rhsMethod.name || *lhsMethod.name == *rhsMethod.name) &&
 				(lhsMethod.pkgPath == rhsMethod.pkgPath || *lhsMethod.pkgPath == *rhsMethod.pkgPath) {
 				break
 			}

 			ri++
 		}

 		if !eqtype(lhsMethod.typ, rhsMethod.mtyp) {
 			m.methods[1] = nil
 			return *lhsMethod.name
 		}

 		if li == 0 {
 			m1 = rhsMethod.tfn // we'll set m.methods[1] at the end
 		} else {
 			methods[li+1] = rhsMethod.tfn
 		}
 		ri++
 	}
 	m.methods[1] = m1
 	return ""
 }

 func iterate_itabs(fn func(*itab)) {
 	// Note: only runs during stop the world or with itabLock held,
 	// so no other locks/atomics needed.
 	t := itabTable
 	for i := uintptr(0); i < t.size; i++ {
 		m := *(**itab)(add(unsafe.Pointer(&t.entries), i*sys.PtrSize))
 		if m != nil {
 			fn(m)
 		}
 	}
 }

 // Return the interface method table for a value of type rhs converted
 // to an interface of type lhs.
 func getitab(lhs, rhs *_type, canfail bool) unsafe.Pointer {
 	if rhs == nil {
 		return nil
 	}

 	if lhs.kind&kindMask != kindInterface {
 		throw("getitab called for non-interface type")
 	}

 	lhsi := (*interfacetype)(unsafe.Pointer(lhs))

 	if len(lhsi.methods) == 0 {
 		throw("getitab called for empty interface type")
 	}

 	if rhs.uncommontype == nil || len(rhs.methods) == 0 {
 		if canfail {
 			return nil
 		}
 		panic(&TypeAssertionError{nil, rhs, lhs, *lhsi.methods[0].name})
 	}

 	var m *itab

 	// First, look in the existing table to see if we can find the itab we need.
 	// This is by far the most common case, so do it without locks.
 	// Use atomic to ensure we see any previous writes done by the thread
 	// that updates the itabTable field (with atomic.Storep in itabAdd).
 	t := (*itabTableType)(atomic.Loadp(unsafe.Pointer(&itabTable)))
 	if m = t.find(lhsi, rhs); m != nil {
 		goto finish
 	}

 	// Not found.  Grab the lock and try again.
 	lockInit(&itabLock, lockRankItab)
 	lock(&itabLock)
 	if m = itabTable.find(lhsi, rhs); m != nil {
 		unlock(&itabLock)
 		goto finish
 	}

 	// Entry doesn't exist yet. Make a new entry & add it.
 	m = (*itab)(persistentalloc(unsafe.Sizeof(itab{})+uintptr(len(lhsi.methods)-1)*sys.PtrSize, 0, &memstats.other_sys))
 	m.inter = lhsi
 	m.methods[0] = unsafe.Pointer(rhs)
 	m.init()
 	itabAdd(m)
 	unlock(&itabLock)
 finish:
 	if m.methods[1] != nil {
 		return unsafe.Pointer(&m.methods[0])
 	}
 	if canfail {
 		return nil
 	}
 	// this can only happen if the conversion
 	// was already done once using the , ok form
 	// and we have a cached negative result.
 	// The cached result doesn't record which
 	// interface function was missing, so initialize
 	// the itab again to get the missing function name.
 	panic(&TypeAssertionError{nil, rhs, lhs, m.init()})
 }

 // Return the interface method table for a value of type rhs converted
 // to an interface of type lhs.  Panics if the conversion is impossible.
 func requireitab(lhs, rhs *_type) unsafe.Pointer {
 	return getitab(lhs, rhs, false)
 }

 // Return the interface method table for a value of type rhs converted
 // to an interface of type lhs.  Panics if the conversion is
 // impossible or if the rhs type is nil.
 func assertitab(lhs, rhs *_type) unsafe.Pointer {
 	if rhs == nil {
 		panic(&TypeAssertionError{nil, nil, lhs, ""})
 	}

 	if lhs.kind&kindMask != kindInterface {
 		throw("assertitab called for non-interface type")
 	}

 	lhsi := (*interfacetype)(unsafe.Pointer(lhs))

 	if len(lhsi.methods) == 0 {
 		return unsafe.Pointer(rhs)
 	}

 	return getitab(lhs, rhs, false)
 }

 // panicdottype is called when doing an i.(T) conversion and the conversion fails.
 func panicdottype(lhs, rhs, inter *_type) {
 	panic(&TypeAssertionError{inter, rhs, lhs, ""})
 }

 // Convert an empty interface to an empty interface, for a comma-ok
 // type assertion.
 func ifaceE2E2(e eface) (eface, bool) {
 	return e, e._type != nil
 }

 // Convert a non-empty interface to an empty interface, for a comma-ok
 // type assertion.
 func ifaceI2E2(i iface) (eface, bool) {
 	if i.tab == nil {
 		return eface{nil, nil}, false
 	} else {
 		return eface{*(**_type)(i.tab), i.data}, true
 	}
 }

 // Convert an empty interface to a non-empty interface, for a comma-ok
 // type assertion.
 func ifaceE2I2(inter *_type, e eface) (iface, bool) {
 	if e._type == nil {
 		return iface{nil, nil}, false
 	} else {
 		itab := getitab(inter, e._type, true)
 		if itab == nil {
 			return iface{nil, nil}, false
 		} else {
 			return iface{itab, e.data}, true
 		}
 	}
 }

 // Convert a non-empty interface to a non-empty interface, for a
 // comma-ok type assertion.
 func ifaceI2I2(inter *_type, i iface) (iface, bool) {
 	if i.tab == nil {
 		return iface{nil, nil}, false
 	} else {
 		itab := getitab(inter, *(**_type)(i.tab), true)
 		if itab == nil {
 			return iface{nil, nil}, false
 		} else {
 			return iface{itab, i.data}, true
 		}
 	}
 }

 // Convert an empty interface to a pointer non-interface type.
 func ifaceE2T2P(t *_type, e eface) (unsafe.Pointer, bool) {
 	if !eqtype(t, e._type) {
 		return nil, false
 	} else {
 		return e.data, true
 	}
 }

 // Convert a non-empty interface to a pointer non-interface type.
 func ifaceI2T2P(t *_type, i iface) (unsafe.Pointer, bool) {
 	if i.tab == nil || !eqtype(t, *(**_type)(i.tab)) {
 		return nil, false
 	} else {
 		return i.data, true
 	}
 }

 // Convert an empty interface to a non-pointer non-interface type.
 func ifaceE2T2(t *_type, e eface, ret unsafe.Pointer) bool {
 	if !eqtype(t, e._type) {
 		typedmemclr(t, ret)
 		return false
 	} else {
 		if isDirectIface(t) {
 			*(*unsafe.Pointer)(ret) = e.data
 		} else {
 			typedmemmove(t, ret, e.data)
 		}
 		return true
 	}
 }

 // Convert a non-empty interface to a non-pointer non-interface type.
 func ifaceI2T2(t *_type, i iface, ret unsafe.Pointer) bool {
 	if i.tab == nil || !eqtype(t, *(**_type)(i.tab)) {
 		typedmemclr(t, ret)
 		return false
 	} else {
 		if isDirectIface(t) {
 			*(*unsafe.Pointer)(ret) = i.data
 		} else {
 			typedmemmove(t, ret, i.data)
 		}
 		return true
 	}
 }

 // Return whether we can convert a type to an interface type.
 func ifaceT2Ip(to, from *_type) bool {
 	if from == nil {
 		return false
 	}

 	if to.kind&kindMask != kindInterface {
 		throw("ifaceT2Ip called with non-interface type")
 	}
 	toi := (*interfacetype)(unsafe.Pointer(to))

 	if from.uncommontype == nil || len(from.methods) == 0 {
 		return len(toi.methods) == 0
 	}

 	ri := 0
 	for li := range toi.methods {
 		toMethod := &toi.methods[li]
 		var fromMethod *method
 		for {
 			if ri >= len(from.methods) {
 				return false
 			}

 			fromMethod = &from.methods[ri]
 			if (toMethod.name == fromMethod.name || *toMethod.name == *fromMethod.name) &&
 				(toMethod.pkgPath == fromMethod.pkgPath || *toMethod.pkgPath == *fromMethod.pkgPath) {
 				break
 			}

 			ri++
 		}

 		if !eqtype(fromMethod.mtyp, toMethod.typ) {
 			return false
 		}

 		ri++
 	}

 	return true
 }

 //go:linkname reflect_ifaceE2I reflect.ifaceE2I
 func reflect_ifaceE2I(inter *interfacetype, e eface, dst *iface) {
 	t := e._type
 	if t == nil {
 		panic(TypeAssertionError{nil, nil, &inter.typ, ""})
 	}
 	dst.tab = requireitab((*_type)(unsafe.Pointer(inter)), t)
 	dst.data = e.data
 }

 //go:linkname reflectlite_ifaceE2I internal_1reflectlite.ifaceE2I
 func reflectlite_ifaceE2I(inter *interfacetype, e eface, dst *iface) {
 	t := e._type
 	if t == nil {
 		panic(TypeAssertionError{nil, nil, &inter.typ, ""})
 	}
 	dst.tab = requireitab((*_type)(unsafe.Pointer(inter)), t)
 	dst.data = e.data
 }

 // staticuint64s is used to avoid allocating in convTx for small integer values.
 var staticuint64s = [...]uint64{
 	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
 	0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
 	0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
 	0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
 	0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
 	0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
 	0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
 	0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
 	0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
 	0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
 	0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57,
 	0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
 	0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
 	0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
 	0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
 	0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
 	0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
 	0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
 	0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
 	0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
 	0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
 	0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
 	0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
 	0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
 	0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
 	0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
 	0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
 	0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
 	0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
 	0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
 	0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
 	0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
 }
	// Copyright 2014 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package runtime

	import (
	"runtime/internal/atomic"
	"runtime/internal/sys"
	"unsafe"
	)

	// For gccgo, use go:linkname to export compiler-called functions.
	//
	//go:linkname requireitab
	//go:linkname assertitab
	//go:linkname panicdottype
	//go:linkname ifaceE2E2
	//go:linkname ifaceI2E2
	//go:linkname ifaceE2I2
	//go:linkname ifaceI2I2
	//go:linkname ifaceE2T2P
	//go:linkname ifaceI2T2P
	//go:linkname ifaceE2T2
	//go:linkname ifaceI2T2
	//go:linkname ifaceT2Ip
	// Temporary for C code to call:
	//go:linkname getitab

	// The gccgo itab structure is different than the gc one.
	//
	// Both gccgo and gc represent empty interfaces the same way:
	// a two field struct, where the first field points to a type descriptor
	// (a *_type) and the second field is the data pointer.
	//
	// Non-empty interfaces are also two-field structs, and the second
	// field is the data pointer. However, for gccgo, the first field, the
	// itab field, is different. The itab field points to the interface
	// method table, which is the implemention of a specific interface
	// type for a specific dynamic non-interface type. An interface
	// method table is a list of pointer values. The first pointer is the
	// type descriptor (a *_type) for the dynamic type. The subsequent
	// pointers are pointers to function code, which implement the methods
	// required by the interface. The pointers are sorted by name.
	//
	// The method pointers in the itab are C function pointers, not Go
	// function pointers; they may be called directly, and they have no
	// closures. The receiver is always passed as a pointer, and it is
	// always the same pointer stored in the interface value. A value
	// method starts by copying the receiver value out of the pointer into
	// a local variable.
	//
	// A method call on an interface value is by definition calling a
	// method at a known index m in the list of methods. Given a non-empty
	// interface value i, the call i.m(args) looks like
	// i.itab[m+1](i.iface, args)

	// Both an empty interface and a non-empty interface have a data
	// pointer field. The meaning of this field is determined by the
	// kindDirectIface bit in the `kind` field of the type descriptor of
	// the value stored in the interface. If kindDirectIface is set, then
	// the data pointer field in the interface value is exactly the value
	// stored in the interface. Otherwise, the data pointer field is a
	// pointer to memory that holds the value. It follows from this that
	// kindDirectIface can only be set for a type whose representation is
	// simply a pointer. In the current gccgo implementation, this is set
	// for types that are pointer-shaped, including unsafe.Pointer, channels,
	// maps, functions, single-field structs and single-element arrays whose
	// single field is simply a pointer-shaped type.

	// For a nil interface value both fields in the interface struct are nil.

	// itabs are statically allocated or persistently allocated. They are
	// never freed. For itabs allocated at run time, they are cached in
	// itabTable, so we reuse the same itab for the same (interface, concrete)
	// type pair. The gc runtime prepopulates the cache with statically
	// allocated itabs. Currently we don't do that as we don't have a way to
	// find all the statically allocated itabs.

	const itabInitSize = 512

	var (
	itabLock mutex // lock for accessing itab table
	itabTable = &itabTableInit // pointer to current table
	itabTableInit = itabTableType{size: itabInitSize} // starter table
	)

	// Cache entry type of itab table.
	// For gccgo, this is not the data type we used in the interface header.
	type itab struct {
	inter *interfacetype
	methods [2]unsafe.Pointer // method table. variable sized. first entry is the type descriptor.
	}

	func (m itab) _type() _type {
	return (*_type)(m.methods[0])
	}

	// Note: change the formula in the mallocgc call in itabAdd if you change these fields.
	type itabTableType struct {
	size uintptr // length of entries array. Always a power of 2.
	count uintptr // current number of filled entries.
	entries [itabInitSize]*itab // really [size] large
	}

	func itabHashFunc(inter interfacetype, typ _type) uintptr {
	// compiler has provided some good hash codes for us.
	return uintptr(inter.typ.hash ^ typ.hash)
	}

	// find finds the given interface/type pair in t.
	// Returns nil if the given interface/type pair isn't present.
	func (t itabTableType) find(inter interfacetype, typ _type) itab {
	// Implemented using quadratic probing.
	// Probe sequence is h(i) = h0 + i*(i+1)/2 mod 2^k.
	// We're guaranteed to hit all table entries using this probe sequence.
	mask := t.size - 1
	h := itabHashFunc(inter, typ) & mask
	for i := uintptr(1); ; i++ {
	p := (*itab)(add(unsafe.Pointer(&t.entries), hsys.PtrSize))
	// Use atomic read here so if we see m != nil, we also see
	// the initializations of the fields of m.
	// m := *p
	m := (*itab)(atomic.Loadp(unsafe.Pointer(p)))
	if m == nil {
	return nil
	}
	if m.inter == inter && m._type() == typ {
	return m
	}
	h += i
	h &= mask
	}
	}

	// itabAdd adds the given itab to the itab hash table.
	// itabLock must be held.
	func itabAdd(m *itab) {
	// Bugs can lead to calling this while mallocing is set,
	// typically because this is called while panicing.
	// Crash reliably, rather than only when we need to grow
	// the hash table.
	if getg().m.mallocing != 0 {
	throw("malloc deadlock")
	}

	t := itabTable
	if t.count >= 3*(t.size/4) { // 75% load factor
	// Grow hash table.
	// t2 = new(itabTableType) + some additional entries
	// We lie and tell malloc we want pointer-free memory because
	// all the pointed-to values are not in the heap.
	t2 := (itabTableType)(mallocgc((2+2t.size)*sys.PtrSize, nil, true))
	t2.size = t.size * 2

	// Copy over entries.
	// Note: while copying, other threads may look for an itab and
	// fail to find it. That's ok, they will then try to get the itab lock
	// and as a consequence wait until this copying is complete.
	iterate_itabs(t2.add)
	if t2.count != t.count {
	throw("mismatched count during itab table copy")
	}
	// Publish new hash table. Use an atomic write: see comment in getitab.
	atomicstorep(unsafe.Pointer(&itabTable), unsafe.Pointer(t2))
	// Adopt the new table as our own.
	t = itabTable
	// Note: the old table can be GC'ed here.
	}
	t.add(m)
	}

	// add adds the given itab to itab table t.
	// itabLock must be held.
	func (t itabTableType) add(m itab) {
	// See comment in find about the probe sequence.
	// Insert new itab in the first empty spot in the probe sequence.
	mask := t.size - 1
	h := itabHashFunc(m.inter, m._type()) & mask
	for i := uintptr(1); ; i++ {
	p := (*itab)(add(unsafe.Pointer(&t.entries), hsys.PtrSize))
	m2 := *p
	if m2 == m {
	// A given itab may be used in more than one module
	// and thanks to the way global symbol resolution works, the
	// pointed-to itab may already have been inserted into the
	// global 'hash'.
	return
	}
	if m2 == nil {
	// Use atomic write here so if a reader sees m, it also
	// sees the correctly initialized fields of m.
	// NoWB is ok because m is not in heap memory.
	// *p = m
	atomic.StorepNoWB(unsafe.Pointer(p), unsafe.Pointer(m))
	t.count++
	return
	}
	h += i
	h &= mask
	}
	}

	// init fills in the m.methods array with all the code pointers for
	// the m.inter/m._type pair. If the type does not implement the interface,
	// it sets m.methods[1] to nil and returns the name of an interface function that is missing.
	// It is ok to call this multiple times on the same m, even concurrently.
	func (m *itab) init() string {
	inter := m.inter
	typ := m._type()
	ni := len(inter.methods) + 1
	methods := (*[1 << 16]unsafe.Pointer)(unsafe.Pointer(&m.methods[0]))[:ni:ni]
	var m1 unsafe.Pointer

	ri := 0
	for li := range inter.methods {
	lhsMethod := &inter.methods[li]
	var rhsMethod *method

	for {
	if ri >= len(typ.methods) {
	m.methods[1] = nil
	return *lhsMethod.name
	}

	rhsMethod = &typ.methods[ri]
	if (lhsMethod.name == rhsMethod.name \|\| lhsMethod.name == rhsMethod.name) &&
	(lhsMethod.pkgPath == rhsMethod.pkgPath \|\| lhsMethod.pkgPath == rhsMethod.pkgPath) {
	break
	}

	ri++
	}

	if !eqtype(lhsMethod.typ, rhsMethod.mtyp) {
	m.methods[1] = nil
	return *lhsMethod.name
	}

	if li == 0 {
	m1 = rhsMethod.tfn // we'll set m.methods[1] at the end
	} else {
	methods[li+1] = rhsMethod.tfn
	}
	ri++
	}
	m.methods[1] = m1
	return ""
	}

	func iterate_itabs(fn func(*itab)) {
	// Note: only runs during stop the world or with itabLock held,
	// so no other locks/atomics needed.
	t := itabTable
	for i := uintptr(0); i < t.size; i++ {
	m := (itab)(add(unsafe.Pointer(&t.entries), isys.PtrSize))
	if m != nil {
	fn(m)
	}
	}
	}

	// Return the interface method table for a value of type rhs converted
	// to an interface of type lhs.
	func getitab(lhs, rhs *_type, canfail bool) unsafe.Pointer {
	if rhs == nil {
	return nil
	}

	if lhs.kind&kindMask != kindInterface {
	throw("getitab called for non-interface type")
	}

	lhsi := (*interfacetype)(unsafe.Pointer(lhs))

	if len(lhsi.methods) == 0 {
	throw("getitab called for empty interface type")
	}

	if rhs.uncommontype == nil \|\| len(rhs.methods) == 0 {
	if canfail {
	return nil
	}
	panic(&TypeAssertionError{nil, rhs, lhs, *lhsi.methods[0].name})
	}

	var m *itab

	// First, look in the existing table to see if we can find the itab we need.
	// This is by far the most common case, so do it without locks.
	// Use atomic to ensure we see any previous writes done by the thread
	// that updates the itabTable field (with atomic.Storep in itabAdd).
	t := (*itabTableType)(atomic.Loadp(unsafe.Pointer(&itabTable)))
	if m = t.find(lhsi, rhs); m != nil {
	goto finish
	}

	// Not found. Grab the lock and try again.
	lockInit(&itabLock, lockRankItab)
	lock(&itabLock)
	if m = itabTable.find(lhsi, rhs); m != nil {
	unlock(&itabLock)
	goto finish
	}

	// Entry doesn't exist yet. Make a new entry & add it.
	m = (itab)(persistentalloc(unsafe.Sizeof(itab{})+uintptr(len(lhsi.methods)-1)sys.PtrSize, 0, &memstats.other_sys))
	m.inter = lhsi
	m.methods[0] = unsafe.Pointer(rhs)
	m.init()
	itabAdd(m)
	unlock(&itabLock)
	finish:
	if m.methods[1] != nil {
	return unsafe.Pointer(&m.methods[0])
	}
	if canfail {
	return nil
	}
	// this can only happen if the conversion
	// was already done once using the , ok form
	// and we have a cached negative result.
	// The cached result doesn't record which
	// interface function was missing, so initialize
	// the itab again to get the missing function name.
	panic(&TypeAssertionError{nil, rhs, lhs, m.init()})
	}

	// Return the interface method table for a value of type rhs converted
	// to an interface of type lhs. Panics if the conversion is impossible.
	func requireitab(lhs, rhs *_type) unsafe.Pointer {
	return getitab(lhs, rhs, false)
	}

	// Return the interface method table for a value of type rhs converted
	// to an interface of type lhs. Panics if the conversion is
	// impossible or if the rhs type is nil.
	func assertitab(lhs, rhs *_type) unsafe.Pointer {
	if rhs == nil {
	panic(&TypeAssertionError{nil, nil, lhs, ""})
	}

	if lhs.kind&kindMask != kindInterface {
	throw("assertitab called for non-interface type")
	}

	lhsi := (*interfacetype)(unsafe.Pointer(lhs))

	if len(lhsi.methods) == 0 {
	return unsafe.Pointer(rhs)
	}

	return getitab(lhs, rhs, false)
	}

	// panicdottype is called when doing an i.(T) conversion and the conversion fails.
	func panicdottype(lhs, rhs, inter *_type) {
	panic(&TypeAssertionError{inter, rhs, lhs, ""})
	}

	// Convert an empty interface to an empty interface, for a comma-ok
	// type assertion.
	func ifaceE2E2(e eface) (eface, bool) {
	return e, e._type != nil
	}

	// Convert a non-empty interface to an empty interface, for a comma-ok
	// type assertion.
	func ifaceI2E2(i iface) (eface, bool) {
	if i.tab == nil {
	return eface{nil, nil}, false
	} else {
	return eface{(*_type)(i.tab), i.data}, true
	}
	}

	// Convert an empty interface to a non-empty interface, for a comma-ok
	// type assertion.
	func ifaceE2I2(inter *_type, e eface) (iface, bool) {
	if e._type == nil {
	return iface{nil, nil}, false
	} else {
	itab := getitab(inter, e._type, true)
	if itab == nil {
	return iface{nil, nil}, false
	} else {
	return iface{itab, e.data}, true
	}
	}
	}

	// Convert a non-empty interface to a non-empty interface, for a
	// comma-ok type assertion.
	func ifaceI2I2(inter *_type, i iface) (iface, bool) {
	if i.tab == nil {
	return iface{nil, nil}, false
	} else {
	itab := getitab(inter, (*_type)(i.tab), true)
	if itab == nil {
	return iface{nil, nil}, false
	} else {
	return iface{itab, i.data}, true
	}
	}
	}

	// Convert an empty interface to a pointer non-interface type.
	func ifaceE2T2P(t *_type, e eface) (unsafe.Pointer, bool) {
	if !eqtype(t, e._type) {
	return nil, false
	} else {
	return e.data, true
	}
	}

	// Convert a non-empty interface to a pointer non-interface type.
	func ifaceI2T2P(t *_type, i iface) (unsafe.Pointer, bool) {
	if i.tab == nil \|\| !eqtype(t, (*_type)(i.tab)) {
	return nil, false
	} else {
	return i.data, true
	}
	}

	// Convert an empty interface to a non-pointer non-interface type.
	func ifaceE2T2(t *_type, e eface, ret unsafe.Pointer) bool {
	if !eqtype(t, e._type) {
	typedmemclr(t, ret)
	return false
	} else {
	if isDirectIface(t) {
	(unsafe.Pointer)(ret) = e.data
	} else {
	typedmemmove(t, ret, e.data)
	}
	return true
	}
	}

	// Convert a non-empty interface to a non-pointer non-interface type.
	func ifaceI2T2(t *_type, i iface, ret unsafe.Pointer) bool {
	if i.tab == nil \|\| !eqtype(t, (*_type)(i.tab)) {
	typedmemclr(t, ret)
	return false
	} else {
	if isDirectIface(t) {
	(unsafe.Pointer)(ret) = i.data
	} else {
	typedmemmove(t, ret, i.data)
	}
	return true
	}
	}

	// Return whether we can convert a type to an interface type.
	func ifaceT2Ip(to, from *_type) bool {
	if from == nil {
	return false
	}

	if to.kind&kindMask != kindInterface {
	throw("ifaceT2Ip called with non-interface type")
	}
	toi := (*interfacetype)(unsafe.Pointer(to))

	if from.uncommontype == nil \|\| len(from.methods) == 0 {
	return len(toi.methods) == 0
	}

	ri := 0
	for li := range toi.methods {
	toMethod := &toi.methods[li]
	var fromMethod *method
	for {
	if ri >= len(from.methods) {
	return false
	}

	fromMethod = &from.methods[ri]
	if (toMethod.name == fromMethod.name \|\| toMethod.name == fromMethod.name) &&
	(toMethod.pkgPath == fromMethod.pkgPath \|\| toMethod.pkgPath == fromMethod.pkgPath) {
	break
	}

	ri++
	}

	if !eqtype(fromMethod.mtyp, toMethod.typ) {
	return false
	}

	ri++
	}

	return true
	}

	//go:linkname reflect_ifaceE2I reflect.ifaceE2I
	func reflect_ifaceE2I(inter interfacetype, e eface, dst iface) {
	t := e._type
	if t == nil {
	panic(TypeAssertionError{nil, nil, &inter.typ, ""})
	}
	dst.tab = requireitab((*_type)(unsafe.Pointer(inter)), t)
	dst.data = e.data
	}

	//go:linkname reflectlite_ifaceE2I internal_1reflectlite.ifaceE2I
	func reflectlite_ifaceE2I(inter interfacetype, e eface, dst iface) {
	t := e._type
	if t == nil {
	panic(TypeAssertionError{nil, nil, &inter.typ, ""})
	}
	dst.tab = requireitab((*_type)(unsafe.Pointer(inter)), t)
	dst.data = e.data
	}

	// staticuint64s is used to avoid allocating in convTx for small integer values.
	var staticuint64s = [...]uint64{
	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
	0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
	0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
	0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
	0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
	0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
	0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
	0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
	0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
	0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f,
	0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57,
	0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
	0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
	0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
	0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
	0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
	0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
	0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
	0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
	0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
	0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
	0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
	0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
	0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
	0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
	0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
	0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
	0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
	0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
	0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
	0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
	0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff,
	}