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// Copyright 2009 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 (
"unsafe"
)
type slice struct {
array unsafe.Pointer
len int
cap int
}
// maxElems is a lookup table containing the maximum capacity for a slice.
// The index is the size of the slice element.
var maxElems = [...]uintptr{
^uintptr(0),
_MaxMem / 1, _MaxMem / 2, _MaxMem / 3, _MaxMem / 4,
_MaxMem / 5, _MaxMem / 6, _MaxMem / 7, _MaxMem / 8,
_MaxMem / 9, _MaxMem / 10, _MaxMem / 11, _MaxMem / 12,
_MaxMem / 13, _MaxMem / 14, _MaxMem / 15, _MaxMem / 16,
_MaxMem / 17, _MaxMem / 18, _MaxMem / 19, _MaxMem / 20,
_MaxMem / 21, _MaxMem / 22, _MaxMem / 23, _MaxMem / 24,
_MaxMem / 25, _MaxMem / 26, _MaxMem / 27, _MaxMem / 28,
_MaxMem / 29, _MaxMem / 30, _MaxMem / 31, _MaxMem / 32,
}
// maxSliceCap returns the maximum capacity for a slice.
func maxSliceCap(elemsize uintptr) uintptr {
if elemsize < uintptr(len(maxElems)) {
return maxElems[elemsize]
}
return _MaxMem / elemsize
}
func makeslice(et *_type, len, cap int) slice {
// NOTE: The len > maxElements check here is not strictly necessary,
// but it produces a 'len out of range' error instead of a 'cap out of range' error
// when someone does make([]T, bignumber). 'cap out of range' is true too,
// but since the cap is only being supplied implicitly, saying len is clearer.
// See issue 4085.
maxElements := maxSliceCap(et.size)
if len < 0 || uintptr(len) > maxElements {
panic(errorString("makeslice: len out of range"))
}
if cap < len || uintptr(cap) > maxElements {
panic(errorString("makeslice: cap out of range"))
}
p := mallocgc(et.size*uintptr(cap), et, true)
return slice{p, len, cap}
}
func makeslice64(et *_type, len64, cap64 int64) slice {
len := int(len64)
if int64(len) != len64 {
panic(errorString("makeslice: len out of range"))
}
cap := int(cap64)
if int64(cap) != cap64 {
panic(errorString("makeslice: cap out of range"))
}
return makeslice(et, len, cap)
}
// growslice handles slice growth during append.
// It is passed the slice element type, the old slice, and the desired new minimum capacity,
// and it returns a new slice with at least that capacity, with the old data
// copied into it.
// The new slice's length is set to the old slice's length,
// NOT to the new requested capacity.
// This is for codegen convenience. The old slice's length is used immediately
// to calculate where to write new values during an append.
// TODO: When the old backend is gone, reconsider this decision.
// The SSA backend might prefer the new length or to return only ptr/cap and save stack space.
func growslice(et *_type, old slice, cap int) slice {
if raceenabled {
callerpc := getcallerpc(unsafe.Pointer(&et))
racereadrangepc(old.array, uintptr(old.len*int(et.size)), callerpc, funcPC(growslice))
}
if msanenabled {
msanread(old.array, uintptr(old.len*int(et.size)))
}
if et.size == 0 {
if cap < old.cap {
panic(errorString("growslice: cap out of range"))
}
// append should not create a slice with nil pointer but non-zero len.
// We assume that append doesn't need to preserve old.array in this case.
return slice{unsafe.Pointer(&zerobase), old.len, cap}
}
newcap := old.cap
doublecap := newcap + newcap
if cap > doublecap {
newcap = cap
} else {
if old.len < 1024 {
newcap = doublecap
} else {
for newcap < cap {
newcap += newcap / 4
}
}
}
var lenmem, newlenmem, capmem uintptr
const ptrSize = unsafe.Sizeof((*byte)(nil))
switch et.size {
case 1:
lenmem = uintptr(old.len)
newlenmem = uintptr(cap)
capmem = roundupsize(uintptr(newcap))
newcap = int(capmem)
case ptrSize:
lenmem = uintptr(old.len) * ptrSize
newlenmem = uintptr(cap) * ptrSize
capmem = roundupsize(uintptr(newcap) * ptrSize)
newcap = int(capmem / ptrSize)
default:
lenmem = uintptr(old.len) * et.size
newlenmem = uintptr(cap) * et.size
capmem = roundupsize(uintptr(newcap) * et.size)
newcap = int(capmem / et.size)
}
if cap < old.cap || uintptr(newcap) > maxSliceCap(et.size) {
panic(errorString("growslice: cap out of range"))
}
var p unsafe.Pointer
if et.kind&kindNoPointers != 0 {
p = mallocgc(capmem, nil, false)
memmove(p, old.array, lenmem)
// The append() that calls growslice is going to overwrite from old.len to cap (which will be the new length).
// Only clear the part that will not be overwritten.
memclrNoHeapPointers(add(p, newlenmem), capmem-newlenmem)
} else {
// Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
p = mallocgc(capmem, et, true)
if !writeBarrier.enabled {
memmove(p, old.array, lenmem)
} else {
for i := uintptr(0); i < lenmem; i += et.size {
typedmemmove(et, add(p, i), add(old.array, i))
}
}
}
return slice{p, old.len, newcap}
}
func slicecopy(to, fm slice, width uintptr) int {
if fm.len == 0 || to.len == 0 {
return 0
}
n := fm.len
if to.len < n {
n = to.len
}
if width == 0 {
return n
}
if raceenabled {
callerpc := getcallerpc(unsafe.Pointer(&to))
pc := funcPC(slicecopy)
racewriterangepc(to.array, uintptr(n*int(width)), callerpc, pc)
racereadrangepc(fm.array, uintptr(n*int(width)), callerpc, pc)
}
if msanenabled {
msanwrite(to.array, uintptr(n*int(width)))
msanread(fm.array, uintptr(n*int(width)))
}
size := uintptr(n) * width
if size == 1 { // common case worth about 2x to do here
// TODO: is this still worth it with new memmove impl?
*(*byte)(to.array) = *(*byte)(fm.array) // known to be a byte pointer
} else {
memmove(to.array, fm.array, size)
}
return n
}
func slicestringcopy(to []byte, fm string) int {
if len(fm) == 0 || len(to) == 0 {
return 0
}
n := len(fm)
if len(to) < n {
n = len(to)
}
if raceenabled {
callerpc := getcallerpc(unsafe.Pointer(&to))
pc := funcPC(slicestringcopy)
racewriterangepc(unsafe.Pointer(&to[0]), uintptr(n), callerpc, pc)
}
if msanenabled {
msanwrite(unsafe.Pointer(&to[0]), uintptr(n))
}
memmove(unsafe.Pointer(&to[0]), stringStructOf(&fm).str, uintptr(n))
return n
}