[dev.simd] simd: added String() method to SIMD vectors.

this required a little plumbing to get access
to the "good" floating point formatting.

Change-Id: Iebec157c28a39df59351bade53b09a3729fc49c0
Reviewed-on: https://go-review.googlesource.com/c/go/+/711781
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/go/build/deps_test.go

@@ -49,11 +49,13 @@ var depsRules = `
 	  internal/coverage/uleb128,
 	  internal/coverage/calloc,
 	  internal/cpu,
+	  internal/ftoa,
 	  internal/goarch,
 	  internal/godebugs,
 	  internal/goexperiment,
 	  internal/goos,
 	  internal/goversion,
+	  internal/itoa,
 	  internal/nettrace,
 	  internal/platform,
 	  internal/profilerecord,
@@ -70,7 +72,7 @@ var depsRules = `
 	internal/goarch < internal/abi;
 	internal/byteorder, internal/cpu, internal/goarch < internal/chacha8rand;
 
-	internal/cpu < simd;
+	internal/cpu, internal/ftoa, internal/itoa < simd;
 
 	# RUNTIME is the core runtime group of packages, all of them very light-weight.
 	internal/abi,
@@ -81,13 +83,13 @@ var depsRules = `
 	internal/godebugs,
 	internal/goexperiment,
 	internal/goos,
+	internal/itoa,
 	internal/profilerecord,
 	internal/trace/tracev2,
 	math/bits,
 	structs
 	< internal/bytealg
 	< internal/stringslite
-	< internal/itoa
 	< internal/unsafeheader
 	< internal/race
 	< internal/msan
@@ -175,7 +177,7 @@ var depsRules = `
 	MATH
 	< runtime/metrics;
 
-	MATH, unicode/utf8
+	MATH, unicode/utf8, internal/ftoa
 	< strconv;
 
 	unicode !< strconv;

src/internal/ftoa/ftoa.go

@@ -0,0 +1,23 @@
+// Copyright 2025 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.
+
+// A hook to get correct floating point conversion from strconv
+// in packages that cannot import strconv.
+
+package ftoa
+
+var formatFloatPtr func(f float64, fmt byte, prec, bitSize int) string
+
+func FormatFloat(f float64, fmt byte, prec, bitSize int) string {
+	if formatFloatPtr != nil {
+		return formatFloatPtr(f, fmt, prec, bitSize)
+	}
+	return "internal/ftoa.formatFloatPtr called before strconv.init()"
+}
+
+func SetFormatFloat(ff func(f float64, fmt byte, prec, bitSize int) string) {
+	if formatFloatPtr == nil {
+		formatFloatPtr = ff
+	}
+}

src/simd/genfiles.go

@@ -263,6 +263,7 @@ func unsafePrologue(s string, out io.Writer) {
 package simd
 
 import "unsafe"
+
 `, s)
 }
 
@@ -795,6 +796,15 @@ func (from {{.Base}}{{.WxC}}) ToMask() (to Mask{{.WxC}}) {
 }
 `)
 
+var stringTemplate = shapedTemplateOf(allShapes, "String methods", `
+// String returns a string representation of SIMD vector x
+func (x {{.VType}}) String() string {
+	var s [{{.Count}}]{{.Etype}}
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+`)
+
 const TD = "internal/simd_test/"
 
 func main() {
@@ -836,6 +846,7 @@ func main() {
 			maskCvtTemplate,
 			bitWiseIntTemplate,
 			bitWiseUintTemplate,
+			stringTemplate,
 		)
 	}
 	if *ush != "" {

src/simd/internal/simd_test/simd_test.go

@@ -1001,3 +1001,32 @@ func TestSelect2FromPairConstGroupedInt512(t *testing.T) {
 	foo(lh, 0, 3)
 	foo(hl, 2, 1)
 }
+
+func TestString(t *testing.T) {
+	x := simd.LoadUint32x4Slice([]uint32{0, 1, 2, 3})
+	y := simd.LoadInt64x4Slice([]int64{-4, -5, -6, -7})
+	z := simd.LoadFloat32x4Slice([]float32{0.5, 1.5, -2.5, 3.5e9})
+	w := simd.LoadFloat64x4Slice([]float64{0.5, 1.5, -2.5, 3.5e9})
+
+	sx := "{0,1,2,3}"
+	sy := "{-4,-5,-6,-7}"
+	sz := "{0.5,1.5,-2.5,3.5e+09}"
+	sw := sz
+
+	if x.String() != sx {
+		t.Errorf("x=%s wanted %s", x, sx)
+	}
+	if y.String() != sy {
+		t.Errorf("y=%s wanted %s", y, sy)
+	}
+	if z.String() != sz {
+		t.Errorf("z=%s wanted %s", z, sz)
+	}
+	if w.String() != sw {
+		t.Errorf("w=%s wanted %s", w, sw)
+	}
+	t.Logf("w=%s", w)
+	t.Logf("x=%s", x)
+	t.Logf("y=%s", y)
+	t.Logf("z=%s", z)
+}

src/simd/other_gen_amd64.go

@@ -591,3 +591,213 @@ func (x Uint32x16) Not() Uint32x16 {
 func (x Uint64x8) Not() Uint64x8 {
 	return x.Xor(x.Equal(x).AsInt64x8().AsUint64x8())
 }
+
+// String returns a string representation of SIMD vector x
+func (x Int8x16) String() string {
+	var s [16]int8
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int16x8) String() string {
+	var s [8]int16
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int32x4) String() string {
+	var s [4]int32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int64x2) String() string {
+	var s [2]int64
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint8x16) String() string {
+	var s [16]uint8
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint16x8) String() string {
+	var s [8]uint16
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint32x4) String() string {
+	var s [4]uint32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint64x2) String() string {
+	var s [2]uint64
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Float32x4) String() string {
+	var s [4]float32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Float64x2) String() string {
+	var s [2]float64
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int8x32) String() string {
+	var s [32]int8
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int16x16) String() string {
+	var s [16]int16
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int32x8) String() string {
+	var s [8]int32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int64x4) String() string {
+	var s [4]int64
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint8x32) String() string {
+	var s [32]uint8
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint16x16) String() string {
+	var s [16]uint16
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint32x8) String() string {
+	var s [8]uint32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint64x4) String() string {
+	var s [4]uint64
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Float32x8) String() string {
+	var s [8]float32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Float64x4) String() string {
+	var s [4]float64
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int8x64) String() string {
+	var s [64]int8
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int16x32) String() string {
+	var s [32]int16
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int32x16) String() string {
+	var s [16]int32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Int64x8) String() string {
+	var s [8]int64
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint8x64) String() string {
+	var s [64]uint8
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint16x32) String() string {
+	var s [32]uint16
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint32x16) String() string {
+	var s [16]uint32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Uint64x8) String() string {
+	var s [8]uint64
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Float32x16) String() string {
+	var s [16]float32
+	x.Store(&s)
+	return sliceToString(s[:])
+}
+
+// String returns a string representation of SIMD vector x
+func (x Float64x8) String() string {
+	var s [8]float64
+	x.Store(&s)
+	return sliceToString(s[:])
+}

src/simd/string.go

@@ -0,0 +1,49 @@
+// Copyright 2025 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.
+
+//go:build goexperiment.simd && amd64
+
+package simd
+
+import (
+	"internal/ftoa"
+	"internal/itoa"
+)
+
+type number interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 | ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr | ~float32 | ~float64
+}
+
+func sliceToString[T number](x []T) string {
+	s := ""
+	pfx := "{"
+	for _, y := range x {
+		s += pfx
+		pfx = ","
+		switch e := any(y).(type) {
+		case int8:
+			s += itoa.Itoa(int(e))
+		case int16:
+			s += itoa.Itoa(int(e))
+		case int32:
+			s += itoa.Itoa(int(e))
+		case int64:
+			s += itoa.Itoa(int(e))
+		case uint8:
+			s += itoa.Uitoa(uint(e))
+		case uint16:
+			s += itoa.Uitoa(uint(e))
+		case uint32:
+			s += itoa.Uitoa(uint(e))
+		case uint64:
+			s += itoa.Uitoa(uint(e))
+		case float32:
+			s += ftoa.FormatFloat(float64(e), 'g', -1, 32)
+		case float64:
+			s += ftoa.FormatFloat(e, 'g', -1, 64)
+		}
+	}
+	s += "}"
+	return s
+}

src/strconv/ftoa.go

@@ -10,7 +10,10 @@
 
 package strconv
 
-import "math"
+import (
+	"internal/ftoa"
+	"math"
+)
 
 // TODO: move elsewhere?
 type floatInfo struct {
@@ -22,6 +25,10 @@ type floatInfo struct {
 var float32info = floatInfo{23, 8, -127}
 var float64info = floatInfo{52, 11, -1023}
 
+func init() {
+	ftoa.SetFormatFloat(FormatFloat)
+}
+
 // FormatFloat converts the floating-point number f to a string,
 // according to the format fmt and precision prec. It rounds the
 // result assuming that the original was obtained from a floating-point