libgo/go/math/big/arith_test.go - gofrontend - Git at Google

 // 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 big

 import (
 	"fmt"
 	"internal/testenv"
 	"math/rand"
 	"strings"
 	"testing"
 )

 var isRaceBuilder = strings.HasSuffix(testenv.Builder(), "-race")

 type funWW func(x, y, c Word) (z1, z0 Word)
 type argWW struct {
 	x, y, c, z1, z0 Word
 }

 var sumWW = []argWW{
 	{0, 0, 0, 0, 0},
 	{0, 1, 0, 0, 1},
 	{0, 0, 1, 0, 1},
 	{0, 1, 1, 0, 2},
 	{12345, 67890, 0, 0, 80235},
 	{12345, 67890, 1, 0, 80236},
 	{_M, 1, 0, 1, 0},
 	{_M, 0, 1, 1, 0},
 	{_M, 1, 1, 1, 1},
 	{_M, _M, 0, 1, _M - 1},
 	{_M, _M, 1, 1, _M},
 }

 func testFunWW(t *testing.T, msg string, f funWW, a argWW) {
 	z1, z0 := f(a.x, a.y, a.c)
 	if z1 != a.z1 || z0 != a.z0 {
 		t.Errorf("%s%+v\n\tgot z1:z0 = %#x:%#x; want %#x:%#x", msg, a, z1, z0, a.z1, a.z0)
 	}
 }

 func TestFunWW(t *testing.T) {
 	for _, a := range sumWW {
 		arg := a
 		testFunWW(t, "addWW_g", addWW_g, arg)

 		arg = argWW{a.y, a.x, a.c, a.z1, a.z0}
 		testFunWW(t, "addWW_g symmetric", addWW_g, arg)

 		arg = argWW{a.z0, a.x, a.c, a.z1, a.y}
 		testFunWW(t, "subWW_g", subWW_g, arg)

 		arg = argWW{a.z0, a.y, a.c, a.z1, a.x}
 		testFunWW(t, "subWW_g symmetric", subWW_g, arg)
 	}
 }

 type funVV func(z, x, y []Word) (c Word)
 type argVV struct {
 	z, x, y nat
 	c       Word
 }

 var sumVV = []argVV{
 	{},
 	{nat{0}, nat{0}, nat{0}, 0},
 	{nat{1}, nat{1}, nat{0}, 0},
 	{nat{0}, nat{_M}, nat{1}, 1},
 	{nat{80235}, nat{12345}, nat{67890}, 0},
 	{nat{_M - 1}, nat{_M}, nat{_M}, 1},
 	{nat{0, 0, 0, 0}, nat{_M, _M, _M, _M}, nat{1, 0, 0, 0}, 1},
 	{nat{0, 0, 0, _M}, nat{_M, _M, _M, _M - 1}, nat{1, 0, 0, 0}, 0},
 	{nat{0, 0, 0, 0}, nat{_M, 0, _M, 0}, nat{1, _M, 0, _M}, 1},
 }

 func testFunVV(t *testing.T, msg string, f funVV, a argVV) {
 	z := make(nat, len(a.z))
 	c := f(z, a.x, a.y)
 	for i, zi := range z {
 		if zi != a.z[i] {
 			t.Errorf("%s%+v\n\tgot z[%d] = %#x; want %#x", msg, a, i, zi, a.z[i])
 			break
 		}
 	}
 	if c != a.c {
 		t.Errorf("%s%+v\n\tgot c = %#x; want %#x", msg, a, c, a.c)
 	}
 }

 func TestFunVV(t *testing.T) {
 	for _, a := range sumVV {
 		arg := a
 		testFunVV(t, "addVV_g", addVV_g, arg)
 		testFunVV(t, "addVV", addVV, arg)

 		arg = argVV{a.z, a.y, a.x, a.c}
 		testFunVV(t, "addVV_g symmetric", addVV_g, arg)
 		testFunVV(t, "addVV symmetric", addVV, arg)

 		arg = argVV{a.x, a.z, a.y, a.c}
 		testFunVV(t, "subVV_g", subVV_g, arg)
 		testFunVV(t, "subVV", subVV, arg)

 		arg = argVV{a.y, a.z, a.x, a.c}
 		testFunVV(t, "subVV_g symmetric", subVV_g, arg)
 		testFunVV(t, "subVV symmetric", subVV, arg)
 	}
 }

 // Always the same seed for reproducible results.
 var rnd = rand.New(rand.NewSource(0))

 func rndW() Word {
 	return Word(rnd.Int63()<<1 | rnd.Int63n(2))
 }

 func rndV(n int) []Word {
 	v := make([]Word, n)
 	for i := range v {
 		v[i] = rndW()
 	}
 	return v
 }

 var benchSizes = []int{1, 2, 3, 4, 5, 1e1, 1e2, 1e3, 1e4, 1e5}

 func BenchmarkAddVV(b *testing.B) {
 	for _, n := range benchSizes {
 		if isRaceBuilder && n > 1e3 {
 			continue
 		}
 		x := rndV(n)
 		y := rndV(n)
 		z := make([]Word, n)
 		b.Run(fmt.Sprint(n), func(b *testing.B) {
 			b.SetBytes(int64(n * _W))
 			for i := 0; i < b.N; i++ {
 				addVV(z, x, y)
 			}
 		})
 	}
 }

 type funVW func(z, x []Word, y Word) (c Word)
 type argVW struct {
 	z, x nat
 	y    Word
 	c    Word
 }

 var sumVW = []argVW{
 	{},
 	{nil, nil, 2, 2},
 	{nat{0}, nat{0}, 0, 0},
 	{nat{1}, nat{0}, 1, 0},
 	{nat{1}, nat{1}, 0, 0},
 	{nat{0}, nat{_M}, 1, 1},
 	{nat{0, 0, 0, 0}, nat{_M, _M, _M, _M}, 1, 1},
 	{nat{585}, nat{314}, 271, 0},
 }

 var lshVW = []argVW{
 	{},
 	{nat{0}, nat{0}, 0, 0},
 	{nat{0}, nat{0}, 1, 0},
 	{nat{0}, nat{0}, 20, 0},

 	{nat{_M}, nat{_M}, 0, 0},
 	{nat{_M << 1 & _M}, nat{_M}, 1, 1},
 	{nat{_M << 20 & _M}, nat{_M}, 20, _M >> (_W - 20)},

 	{nat{_M, _M, _M}, nat{_M, _M, _M}, 0, 0},
 	{nat{_M << 1 & _M, _M, _M}, nat{_M, _M, _M}, 1, 1},
 	{nat{_M << 20 & _M, _M, _M}, nat{_M, _M, _M}, 20, _M >> (_W - 20)},
 }

 var rshVW = []argVW{
 	{},
 	{nat{0}, nat{0}, 0, 0},
 	{nat{0}, nat{0}, 1, 0},
 	{nat{0}, nat{0}, 20, 0},

 	{nat{_M}, nat{_M}, 0, 0},
 	{nat{_M >> 1}, nat{_M}, 1, _M << (_W - 1) & _M},
 	{nat{_M >> 20}, nat{_M}, 20, _M << (_W - 20) & _M},

 	{nat{_M, _M, _M}, nat{_M, _M, _M}, 0, 0},
 	{nat{_M, _M, _M >> 1}, nat{_M, _M, _M}, 1, _M << (_W - 1) & _M},
 	{nat{_M, _M, _M >> 20}, nat{_M, _M, _M}, 20, _M << (_W - 20) & _M},
 }

 func testFunVW(t *testing.T, msg string, f funVW, a argVW) {
 	z := make(nat, len(a.z))
 	c := f(z, a.x, a.y)
 	for i, zi := range z {
 		if zi != a.z[i] {
 			t.Errorf("%s%+v\n\tgot z[%d] = %#x; want %#x", msg, a, i, zi, a.z[i])
 			break
 		}
 	}
 	if c != a.c {
 		t.Errorf("%s%+v\n\tgot c = %#x; want %#x", msg, a, c, a.c)
 	}
 }

 func makeFunVW(f func(z, x []Word, s uint) (c Word)) funVW {
 	return func(z, x []Word, s Word) (c Word) {
 		return f(z, x, uint(s))
 	}
 }

 func TestFunVW(t *testing.T) {
 	for _, a := range sumVW {
 		arg := a
 		testFunVW(t, "addVW_g", addVW_g, arg)
 		testFunVW(t, "addVW", addVW, arg)

 		arg = argVW{a.x, a.z, a.y, a.c}
 		testFunVW(t, "subVW_g", subVW_g, arg)
 		testFunVW(t, "subVW", subVW, arg)
 	}

 	shlVW_g := makeFunVW(shlVU_g)
 	shlVW := makeFunVW(shlVU)
 	for _, a := range lshVW {
 		arg := a
 		testFunVW(t, "shlVU_g", shlVW_g, arg)
 		testFunVW(t, "shlVU", shlVW, arg)
 	}

 	shrVW_g := makeFunVW(shrVU_g)
 	shrVW := makeFunVW(shrVU)
 	for _, a := range rshVW {
 		arg := a
 		testFunVW(t, "shrVU_g", shrVW_g, arg)
 		testFunVW(t, "shrVU", shrVW, arg)
 	}
 }

 func BenchmarkAddVW(b *testing.B) {
 	for _, n := range benchSizes {
 		if isRaceBuilder && n > 1e3 {
 			continue
 		}
 		x := rndV(n)
 		y := rndW()
 		z := make([]Word, n)
 		b.Run(fmt.Sprint(n), func(b *testing.B) {
 			b.SetBytes(int64(n * _S))
 			for i := 0; i < b.N; i++ {
 				addVW(z, x, y)
 			}
 		})
 	}
 }

 type funVWW func(z, x []Word, y, r Word) (c Word)
 type argVWW struct {
 	z, x nat
 	y, r Word
 	c    Word
 }

 var prodVWW = []argVWW{
 	{},
 	{nat{0}, nat{0}, 0, 0, 0},
 	{nat{991}, nat{0}, 0, 991, 0},
 	{nat{0}, nat{_M}, 0, 0, 0},
 	{nat{991}, nat{_M}, 0, 991, 0},
 	{nat{0}, nat{0}, _M, 0, 0},
 	{nat{991}, nat{0}, _M, 991, 0},
 	{nat{1}, nat{1}, 1, 0, 0},
 	{nat{992}, nat{1}, 1, 991, 0},
 	{nat{22793}, nat{991}, 23, 0, 0},
 	{nat{22800}, nat{991}, 23, 7, 0},
 	{nat{0, 0, 0, 22793}, nat{0, 0, 0, 991}, 23, 0, 0},
 	{nat{7, 0, 0, 22793}, nat{0, 0, 0, 991}, 23, 7, 0},
 	{nat{0, 0, 0, 0}, nat{7893475, 7395495, 798547395, 68943}, 0, 0, 0},
 	{nat{991, 0, 0, 0}, nat{7893475, 7395495, 798547395, 68943}, 0, 991, 0},
 	{nat{0, 0, 0, 0}, nat{0, 0, 0, 0}, 894375984, 0, 0},
 	{nat{991, 0, 0, 0}, nat{0, 0, 0, 0}, 894375984, 991, 0},
 	{nat{_M << 1 & _M}, nat{_M}, 1 << 1, 0, _M >> (_W - 1)},
 	{nat{_M<<1&_M + 1}, nat{_M}, 1 << 1, 1, _M >> (_W - 1)},
 	{nat{_M << 7 & _M}, nat{_M}, 1 << 7, 0, _M >> (_W - 7)},
 	{nat{_M<<7&_M + 1<<6}, nat{_M}, 1 << 7, 1 << 6, _M >> (_W - 7)},
 	{nat{_M << 7 & _M, _M, _M, _M}, nat{_M, _M, _M, _M}, 1 << 7, 0, _M >> (_W - 7)},
 	{nat{_M<<7&_M + 1<<6, _M, _M, _M}, nat{_M, _M, _M, _M}, 1 << 7, 1 << 6, _M >> (_W - 7)},
 }

 func testFunVWW(t *testing.T, msg string, f funVWW, a argVWW) {
 	z := make(nat, len(a.z))
 	c := f(z, a.x, a.y, a.r)
 	for i, zi := range z {
 		if zi != a.z[i] {
 			t.Errorf("%s%+v\n\tgot z[%d] = %#x; want %#x", msg, a, i, zi, a.z[i])
 			break
 		}
 	}
 	if c != a.c {
 		t.Errorf("%s%+v\n\tgot c = %#x; want %#x", msg, a, c, a.c)
 	}
 }

 // TODO(gri) mulAddVWW and divWVW are symmetric operations but
 //           their signature is not symmetric. Try to unify.

 type funWVW func(z []Word, xn Word, x []Word, y Word) (r Word)
 type argWVW struct {
 	z  nat
 	xn Word
 	x  nat
 	y  Word
 	r  Word
 }

 func testFunWVW(t *testing.T, msg string, f funWVW, a argWVW) {
 	z := make(nat, len(a.z))
 	r := f(z, a.xn, a.x, a.y)
 	for i, zi := range z {
 		if zi != a.z[i] {
 			t.Errorf("%s%+v\n\tgot z[%d] = %#x; want %#x", msg, a, i, zi, a.z[i])
 			break
 		}
 	}
 	if r != a.r {
 		t.Errorf("%s%+v\n\tgot r = %#x; want %#x", msg, a, r, a.r)
 	}
 }

 func TestFunVWW(t *testing.T) {
 	for _, a := range prodVWW {
 		arg := a
 		testFunVWW(t, "mulAddVWW_g", mulAddVWW_g, arg)
 		testFunVWW(t, "mulAddVWW", mulAddVWW, arg)

 		if a.y != 0 && a.r < a.y {
 			arg := argWVW{a.x, a.c, a.z, a.y, a.r}
 			testFunWVW(t, "divWVW_g", divWVW_g, arg)
 			testFunWVW(t, "divWVW", divWVW, arg)
 		}
 	}
 }

 var mulWWTests = []struct {
 	x, y Word
 	q, r Word
 }{
 	{_M, _M, _M - 1, 1},
 	// 32 bit only: {0xc47dfa8c, 50911, 0x98a4, 0x998587f4},
 }

 func TestMulWW(t *testing.T) {
 	for i, test := range mulWWTests {
 		q, r := mulWW_g(test.x, test.y)
 		if q != test.q || r != test.r {
 			t.Errorf("#%d got (%x, %x) want (%x, %x)", i, q, r, test.q, test.r)
 		}
 	}
 }

 var mulAddWWWTests = []struct {
 	x, y, c Word
 	q, r    Word
 }{
 	// TODO(agl): These will only work on 64-bit platforms.
 	// {15064310297182388543, 0xe7df04d2d35d5d80, 13537600649892366549, 13644450054494335067, 10832252001440893781},
 	// {15064310297182388543, 0xdab2f18048baa68d, 13644450054494335067, 12869334219691522700, 14233854684711418382},
 	{_M, _M, 0, _M - 1, 1},
 	{_M, _M, _M, _M, 0},
 }

 func TestMulAddWWW(t *testing.T) {
 	for i, test := range mulAddWWWTests {
 		q, r := mulAddWWW_g(test.x, test.y, test.c)
 		if q != test.q || r != test.r {
 			t.Errorf("#%d got (%x, %x) want (%x, %x)", i, q, r, test.q, test.r)
 		}
 	}
 }

 func BenchmarkAddMulVVW(b *testing.B) {
 	for _, n := range benchSizes {
 		if isRaceBuilder && n > 1e3 {
 			continue
 		}
 		x := rndV(n)
 		y := rndW()
 		z := make([]Word, n)
 		b.Run(fmt.Sprint(n), func(b *testing.B) {
 			b.SetBytes(int64(n * _W))
 			for i := 0; i < b.N; i++ {
 				addMulVVW(z, x, y)
 			}
 		})
 	}
 }

 func testWordBitLen(t *testing.T, fname string, f func(Word) int) {
 	for i := 0; i <= _W; i++ {
 		x := Word(1) << uint(i-1) // i == 0 => x == 0
 		n := f(x)
 		if n != i {
 			t.Errorf("got %d; want %d for %s(%#x)", n, i, fname, x)
 		}
 	}
 }

 func TestWordBitLen(t *testing.T) {
 	testWordBitLen(t, "bitLen", bitLen)
 	testWordBitLen(t, "bitLen_g", bitLen_g)
 }

 // runs b.N iterations of bitLen called on a Word containing (1 << nbits)-1.
 func BenchmarkBitLen(b *testing.B) {
 	// Individual bitLen tests. Numbers chosen to examine both sides
 	// of powers-of-two boundaries.
 	for _, nbits := range []uint{0, 1, 2, 3, 4, 5, 8, 9, 16, 17, 31} {
 		testword := Word((uint64(1) << nbits) - 1)
 		b.Run(fmt.Sprint(nbits), func(b *testing.B) {
 			for i := 0; i < b.N; i++ {
 				bitLen(testword)
 			}
 		})
 	}
 }
	// 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 big

	import (
	"fmt"
	"internal/testenv"
	"math/rand"
	"strings"
	"testing"
	)

	var isRaceBuilder = strings.HasSuffix(testenv.Builder(), "-race")

	type funWW func(x, y, c Word) (z1, z0 Word)
	type argWW struct {
	x, y, c, z1, z0 Word
	}

	var sumWW = []argWW{
	{0, 0, 0, 0, 0},
	{0, 1, 0, 0, 1},
	{0, 0, 1, 0, 1},
	{0, 1, 1, 0, 2},
	{12345, 67890, 0, 0, 80235},
	{12345, 67890, 1, 0, 80236},
	{_M, 1, 0, 1, 0},
	{_M, 0, 1, 1, 0},
	{_M, 1, 1, 1, 1},
	{_M, _M, 0, 1, _M - 1},
	{_M, _M, 1, 1, _M},
	}

	func testFunWW(t *testing.T, msg string, f funWW, a argWW) {
	z1, z0 := f(a.x, a.y, a.c)
	if z1 != a.z1 \|\| z0 != a.z0 {
	t.Errorf("%s%+v\n\tgot z1:z0 = %#x:%#x; want %#x:%#x", msg, a, z1, z0, a.z1, a.z0)
	}
	}

	func TestFunWW(t *testing.T) {
	for _, a := range sumWW {
	arg := a
	testFunWW(t, "addWW_g", addWW_g, arg)

	arg = argWW{a.y, a.x, a.c, a.z1, a.z0}
	testFunWW(t, "addWW_g symmetric", addWW_g, arg)

	arg = argWW{a.z0, a.x, a.c, a.z1, a.y}
	testFunWW(t, "subWW_g", subWW_g, arg)

	arg = argWW{a.z0, a.y, a.c, a.z1, a.x}
	testFunWW(t, "subWW_g symmetric", subWW_g, arg)
	}
	}

	type funVV func(z, x, y []Word) (c Word)
	type argVV struct {
	z, x, y nat
	c Word
	}

	var sumVV = []argVV{
	{},
	{nat{0}, nat{0}, nat{0}, 0},
	{nat{1}, nat{1}, nat{0}, 0},
	{nat{0}, nat{_M}, nat{1}, 1},
	{nat{80235}, nat{12345}, nat{67890}, 0},
	{nat{_M - 1}, nat{_M}, nat{_M}, 1},
	{nat{0, 0, 0, 0}, nat{_M, _M, _M, _M}, nat{1, 0, 0, 0}, 1},
	{nat{0, 0, 0, _M}, nat{_M, _M, _M, _M - 1}, nat{1, 0, 0, 0}, 0},
	{nat{0, 0, 0, 0}, nat{_M, 0, _M, 0}, nat{1, _M, 0, _M}, 1},
	}

	func testFunVV(t *testing.T, msg string, f funVV, a argVV) {
	z := make(nat, len(a.z))
	c := f(z, a.x, a.y)
	for i, zi := range z {
	if zi != a.z[i] {
	t.Errorf("%s%+v\n\tgot z[%d] = %#x; want %#x", msg, a, i, zi, a.z[i])
	break
	}
	}
	if c != a.c {
	t.Errorf("%s%+v\n\tgot c = %#x; want %#x", msg, a, c, a.c)
	}
	}

	func TestFunVV(t *testing.T) {
	for _, a := range sumVV {
	arg := a
	testFunVV(t, "addVV_g", addVV_g, arg)
	testFunVV(t, "addVV", addVV, arg)

	arg = argVV{a.z, a.y, a.x, a.c}
	testFunVV(t, "addVV_g symmetric", addVV_g, arg)
	testFunVV(t, "addVV symmetric", addVV, arg)

	arg = argVV{a.x, a.z, a.y, a.c}
	testFunVV(t, "subVV_g", subVV_g, arg)
	testFunVV(t, "subVV", subVV, arg)

	arg = argVV{a.y, a.z, a.x, a.c}
	testFunVV(t, "subVV_g symmetric", subVV_g, arg)
	testFunVV(t, "subVV symmetric", subVV, arg)
	}
	}

	// Always the same seed for reproducible results.
	var rnd = rand.New(rand.NewSource(0))

	func rndW() Word {
	return Word(rnd.Int63()<<1 \| rnd.Int63n(2))
	}

	func rndV(n int) []Word {
	v := make([]Word, n)
	for i := range v {
	v[i] = rndW()
	}
	return v
	}

	var benchSizes = []int{1, 2, 3, 4, 5, 1e1, 1e2, 1e3, 1e4, 1e5}

	func BenchmarkAddVV(b *testing.B) {
	for _, n := range benchSizes {
	if isRaceBuilder && n > 1e3 {
	continue
	}
	x := rndV(n)
	y := rndV(n)
	z := make([]Word, n)
	b.Run(fmt.Sprint(n), func(b *testing.B) {
	b.SetBytes(int64(n * _W))
	for i := 0; i < b.N; i++ {
	addVV(z, x, y)
	}
	})
	}
	}

	type funVW func(z, x []Word, y Word) (c Word)
	type argVW struct {
	z, x nat
	y Word
	c Word
	}

	var sumVW = []argVW{
	{},
	{nil, nil, 2, 2},
	{nat{0}, nat{0}, 0, 0},
	{nat{1}, nat{0}, 1, 0},
	{nat{1}, nat{1}, 0, 0},
	{nat{0}, nat{_M}, 1, 1},
	{nat{0, 0, 0, 0}, nat{_M, _M, _M, _M}, 1, 1},
	{nat{585}, nat{314}, 271, 0},
	}

	var lshVW = []argVW{
	{},
	{nat{0}, nat{0}, 0, 0},
	{nat{0}, nat{0}, 1, 0},
	{nat{0}, nat{0}, 20, 0},

	{nat{_M}, nat{_M}, 0, 0},
	{nat{_M << 1 & _M}, nat{_M}, 1, 1},
	{nat{_M << 20 & _M}, nat{_M}, 20, _M >> (_W - 20)},

	{nat{_M, _M, _M}, nat{_M, _M, _M}, 0, 0},
	{nat{_M << 1 & _M, _M, _M}, nat{_M, _M, _M}, 1, 1},
	{nat{_M << 20 & _M, _M, _M}, nat{_M, _M, _M}, 20, _M >> (_W - 20)},
	}

	var rshVW = []argVW{
	{},
	{nat{0}, nat{0}, 0, 0},
	{nat{0}, nat{0}, 1, 0},
	{nat{0}, nat{0}, 20, 0},

	{nat{_M}, nat{_M}, 0, 0},
	{nat{_M >> 1}, nat{_M}, 1, _M << (_W - 1) & _M},
	{nat{_M >> 20}, nat{_M}, 20, _M << (_W - 20) & _M},

	{nat{_M, _M, _M}, nat{_M, _M, _M}, 0, 0},
	{nat{_M, _M, _M >> 1}, nat{_M, _M, _M}, 1, _M << (_W - 1) & _M},
	{nat{_M, _M, _M >> 20}, nat{_M, _M, _M}, 20, _M << (_W - 20) & _M},
	}

	func testFunVW(t *testing.T, msg string, f funVW, a argVW) {
	z := make(nat, len(a.z))
	c := f(z, a.x, a.y)
	for i, zi := range z {
	if zi != a.z[i] {
	t.Errorf("%s%+v\n\tgot z[%d] = %#x; want %#x", msg, a, i, zi, a.z[i])
	break
	}
	}
	if c != a.c {
	t.Errorf("%s%+v\n\tgot c = %#x; want %#x", msg, a, c, a.c)
	}
	}

	func makeFunVW(f func(z, x []Word, s uint) (c Word)) funVW {
	return func(z, x []Word, s Word) (c Word) {
	return f(z, x, uint(s))
	}
	}

	func TestFunVW(t *testing.T) {
	for _, a := range sumVW {
	arg := a
	testFunVW(t, "addVW_g", addVW_g, arg)
	testFunVW(t, "addVW", addVW, arg)

	arg = argVW{a.x, a.z, a.y, a.c}
	testFunVW(t, "subVW_g", subVW_g, arg)
	testFunVW(t, "subVW", subVW, arg)
	}

	shlVW_g := makeFunVW(shlVU_g)
	shlVW := makeFunVW(shlVU)
	for _, a := range lshVW {
	arg := a
	testFunVW(t, "shlVU_g", shlVW_g, arg)
	testFunVW(t, "shlVU", shlVW, arg)
	}

	shrVW_g := makeFunVW(shrVU_g)
	shrVW := makeFunVW(shrVU)
	for _, a := range rshVW {
	arg := a
	testFunVW(t, "shrVU_g", shrVW_g, arg)
	testFunVW(t, "shrVU", shrVW, arg)
	}
	}

	func BenchmarkAddVW(b *testing.B) {
	for _, n := range benchSizes {
	if isRaceBuilder && n > 1e3 {
	continue
	}
	x := rndV(n)
	y := rndW()
	z := make([]Word, n)
	b.Run(fmt.Sprint(n), func(b *testing.B) {
	b.SetBytes(int64(n * _S))
	for i := 0; i < b.N; i++ {
	addVW(z, x, y)
	}
	})
	}
	}

	type funVWW func(z, x []Word, y, r Word) (c Word)
	type argVWW struct {
	z, x nat
	y, r Word
	c Word
	}

	var prodVWW = []argVWW{
	{},
	{nat{0}, nat{0}, 0, 0, 0},
	{nat{991}, nat{0}, 0, 991, 0},
	{nat{0}, nat{_M}, 0, 0, 0},
	{nat{991}, nat{_M}, 0, 991, 0},
	{nat{0}, nat{0}, _M, 0, 0},
	{nat{991}, nat{0}, _M, 991, 0},
	{nat{1}, nat{1}, 1, 0, 0},
	{nat{992}, nat{1}, 1, 991, 0},
	{nat{22793}, nat{991}, 23, 0, 0},
	{nat{22800}, nat{991}, 23, 7, 0},
	{nat{0, 0, 0, 22793}, nat{0, 0, 0, 991}, 23, 0, 0},
	{nat{7, 0, 0, 22793}, nat{0, 0, 0, 991}, 23, 7, 0},
	{nat{0, 0, 0, 0}, nat{7893475, 7395495, 798547395, 68943}, 0, 0, 0},
	{nat{991, 0, 0, 0}, nat{7893475, 7395495, 798547395, 68943}, 0, 991, 0},
	{nat{0, 0, 0, 0}, nat{0, 0, 0, 0}, 894375984, 0, 0},
	{nat{991, 0, 0, 0}, nat{0, 0, 0, 0}, 894375984, 991, 0},
	{nat{_M << 1 & _M}, nat{_M}, 1 << 1, 0, _M >> (_W - 1)},
	{nat{_M<<1&_M + 1}, nat{_M}, 1 << 1, 1, _M >> (_W - 1)},
	{nat{_M << 7 & _M}, nat{_M}, 1 << 7, 0, _M >> (_W - 7)},
	{nat{_M<<7&_M + 1<<6}, nat{_M}, 1 << 7, 1 << 6, _M >> (_W - 7)},
	{nat{_M << 7 & _M, _M, _M, _M}, nat{_M, _M, _M, _M}, 1 << 7, 0, _M >> (_W - 7)},
	{nat{_M<<7&_M + 1<<6, _M, _M, _M}, nat{_M, _M, _M, _M}, 1 << 7, 1 << 6, _M >> (_W - 7)},
	}

	func testFunVWW(t *testing.T, msg string, f funVWW, a argVWW) {
	z := make(nat, len(a.z))
	c := f(z, a.x, a.y, a.r)
	for i, zi := range z {
	if zi != a.z[i] {
	t.Errorf("%s%+v\n\tgot z[%d] = %#x; want %#x", msg, a, i, zi, a.z[i])
	break
	}
	}
	if c != a.c {
	t.Errorf("%s%+v\n\tgot c = %#x; want %#x", msg, a, c, a.c)
	}
	}

	// TODO(gri) mulAddVWW and divWVW are symmetric operations but
	// their signature is not symmetric. Try to unify.

	type funWVW func(z []Word, xn Word, x []Word, y Word) (r Word)
	type argWVW struct {
	z nat
	xn Word
	x nat
	y Word
	r Word
	}

	func testFunWVW(t *testing.T, msg string, f funWVW, a argWVW) {
	z := make(nat, len(a.z))
	r := f(z, a.xn, a.x, a.y)
	for i, zi := range z {
	if zi != a.z[i] {
	t.Errorf("%s%+v\n\tgot z[%d] = %#x; want %#x", msg, a, i, zi, a.z[i])
	break
	}
	}
	if r != a.r {
	t.Errorf("%s%+v\n\tgot r = %#x; want %#x", msg, a, r, a.r)
	}
	}

	func TestFunVWW(t *testing.T) {
	for _, a := range prodVWW {
	arg := a
	testFunVWW(t, "mulAddVWW_g", mulAddVWW_g, arg)
	testFunVWW(t, "mulAddVWW", mulAddVWW, arg)

	if a.y != 0 && a.r < a.y {
	arg := argWVW{a.x, a.c, a.z, a.y, a.r}
	testFunWVW(t, "divWVW_g", divWVW_g, arg)
	testFunWVW(t, "divWVW", divWVW, arg)
	}
	}
	}

	var mulWWTests = []struct {
	x, y Word
	q, r Word
	}{
	{_M, _M, _M - 1, 1},
	// 32 bit only: {0xc47dfa8c, 50911, 0x98a4, 0x998587f4},
	}

	func TestMulWW(t *testing.T) {
	for i, test := range mulWWTests {
	q, r := mulWW_g(test.x, test.y)
	if q != test.q \|\| r != test.r {
	t.Errorf("#%d got (%x, %x) want (%x, %x)", i, q, r, test.q, test.r)
	}
	}
	}

	var mulAddWWWTests = []struct {
	x, y, c Word
	q, r Word
	}{
	// TODO(agl): These will only work on 64-bit platforms.
	// {15064310297182388543, 0xe7df04d2d35d5d80, 13537600649892366549, 13644450054494335067, 10832252001440893781},
	// {15064310297182388543, 0xdab2f18048baa68d, 13644450054494335067, 12869334219691522700, 14233854684711418382},
	{_M, _M, 0, _M - 1, 1},
	{_M, _M, _M, _M, 0},
	}

	func TestMulAddWWW(t *testing.T) {
	for i, test := range mulAddWWWTests {
	q, r := mulAddWWW_g(test.x, test.y, test.c)
	if q != test.q \|\| r != test.r {
	t.Errorf("#%d got (%x, %x) want (%x, %x)", i, q, r, test.q, test.r)
	}
	}
	}

	func BenchmarkAddMulVVW(b *testing.B) {
	for _, n := range benchSizes {
	if isRaceBuilder && n > 1e3 {
	continue
	}
	x := rndV(n)
	y := rndW()
	z := make([]Word, n)
	b.Run(fmt.Sprint(n), func(b *testing.B) {
	b.SetBytes(int64(n * _W))
	for i := 0; i < b.N; i++ {
	addMulVVW(z, x, y)
	}
	})
	}
	}

	func testWordBitLen(t *testing.T, fname string, f func(Word) int) {
	for i := 0; i <= _W; i++ {
	x := Word(1) << uint(i-1) // i == 0 => x == 0
	n := f(x)
	if n != i {
	t.Errorf("got %d; want %d for %s(%#x)", n, i, fname, x)
	}
	}
	}

	func TestWordBitLen(t *testing.T) {
	testWordBitLen(t, "bitLen", bitLen)
	testWordBitLen(t, "bitLen_g", bitLen_g)
	}

	// runs b.N iterations of bitLen called on a Word containing (1 << nbits)-1.
	func BenchmarkBitLen(b *testing.B) {
	// Individual bitLen tests. Numbers chosen to examine both sides
	// of powers-of-two boundaries.
	for _, nbits := range []uint{0, 1, 2, 3, 4, 5, 8, 9, 16, 17, 31} {
	testword := Word((uint64(1) << nbits) - 1)
	b.Run(fmt.Sprint(nbits), func(b *testing.B) {
	for i := 0; i < b.N; i++ {
	bitLen(testword)
	}
	})
	}
	}