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moremath: align NaN handling with amd64/arm64 compilers (#705)

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Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>
This commit is contained in:
Takeshi Yoneda
2022-07-21 12:03:05 +09:00
committed by GitHub
parent 0da1af2d51
commit 303b14e67c
2 changed files with 154 additions and 90 deletions
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176
internal/moremath/moremath.go
View File

@@ -19,64 +19,20 @@ const (
// F32ExponentMask is used to extract the exponent of 32-bit floating point.
F32ExponentMask = uint32(0x7f80_0000)
// F32ArithmeticNaNBits is an example 32-bit arithmetic NaN.
F32ArithmeticNaNBits = F32CanonicalNaNBits | 0b1 // Set first bit to make this as an arithmetic NaN.
F32ArithmeticNaNBits = F32CanonicalNaNBits | 0b1 // Set first bit to make this different from the canonical NaN.
// F64ArithmeticNaNPayloadMSB is used to extract the most significant bit of payload of 64-bit arithmetic NaN values
F64ArithmeticNaNPayloadMSB = uint64(0x0008_0000_0000_0000)
// F64ExponentMask is used to extract the exponent of 64-bit floating point.
F64ExponentMask = uint64(0x7ff0_0000_0000_0000)
// F64ArithmeticNaNBits is an example 64-bit arithmetic NaN.
F64ArithmeticNaNBits = F64CanonicalNaNBits | 0b1 // Set first bit to make this as an arithmetic NaN.
F64ArithmeticNaNBits = F64CanonicalNaNBits | 0b1 // Set first bit to make this different from the canonical NaN.
)
// f64ReturnNaNBinOp returns a 64-bit NaN value following the NaN propagation procedure as in
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func f64ReturnNaNBinOp(xb, yb uint64) float64 {
if (xb&F64CanonicalNaNBitsMask == F64CanonicalNaNBits) || (yb&F64CanonicalNaNBitsMask == F64CanonicalNaNBits) {
return math.Float64frombits(F64CanonicalNaNBits)
}
// This case, we can return *one of* arithmetic value (meaning that this is un-deterministic as pointed by Wasm spec).
// Here, we return the fixed F64ArithmeticNaNBits to have determinism.
return math.Float64frombits(F64ArithmeticNaNBits)
}
// f64ReturnNaNUniOp returns a 64-bit NaN value following the NaN propagation procedure as in
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func f64ReturnNaNUniOp(xb uint64) float64 {
if xb&F64CanonicalNaNBitsMask == F64CanonicalNaNBits {
return math.Float64frombits(F64CanonicalNaNBits)
}
// This case, we can return *one of* arithmetic value (meaning that this is un-deterministic as pointed by Wasm spec).
// Here, we return the fixed F64ArithmeticNaNBits to have determinism.
return math.Float64frombits(F64ArithmeticNaNBits)
}
// f32ReturnNaNBinOp returns a 32-bit NaN value following the NaN propagation procedure as in
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func f32ReturnNaNBinOp(xb, yb uint32) float32 {
if (xb&F32CanonicalNaNBitsMask == F32CanonicalNaNBits) || (yb&F32CanonicalNaNBitsMask == F32CanonicalNaNBits) {
return math.Float32frombits(F32CanonicalNaNBits)
}
// This case, we can return *one of* arithmetic value (meaning that this is un-deterministic as pointed by Wasm spec).
// Here, we return the fixed F32ArithmeticNaNBits to have determinism.
return math.Float32frombits(F32ArithmeticNaNBits)
}
// f32ReturnNaNUniOp returns a 32-bit NaN value following the NaN propagation procedure as in
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func f32ReturnNaNUniOp(xb uint32) float32 {
if xb&F32CanonicalNaNBitsMask == F32CanonicalNaNBits {
return math.Float32frombits(F32CanonicalNaNBits)
}
// This case, we can return *one of* arithmetic value (meaning that this is un-deterministic as pointed by Wasm spec).
// Here, we return the fixed F32ArithmeticNaNBits to have determinism.
return math.Float32frombits(F32ArithmeticNaNBits)
}
// WasmCompatMin64 is the Wasm spec compatible variant of math.Min for 64-bit floating points.
func WasmCompatMin64(x, y float64) float64 {
switch {
case math.IsNaN(x) || math.IsNaN(y):
return f64ReturnNaNBinOp(math.Float64bits(x), math.Float64bits(y))
return returnF64NaNBinOp(x, y)
case math.IsInf(x, -1) || math.IsInf(y, -1):
return math.Inf(-1)
case x == 0 && x == y:
@@ -96,7 +52,7 @@ func WasmCompatMin32(x, y float32) float32 {
x64, y64 := float64(x), float64(y)
switch {
case math.IsNaN(x64) || math.IsNaN(y64):
return f32ReturnNaNBinOp(math.Float32bits(x), math.Float32bits(y))
return returnF32NaNBinOp(x, y)
case math.IsInf(x64, -1) || math.IsInf(y64, -1):
return float32(math.Inf(-1))
case x == 0 && x == y:
@@ -115,7 +71,7 @@ func WasmCompatMin32(x, y float32) float32 {
func WasmCompatMax64(x, y float64) float64 {
switch {
case math.IsNaN(x) || math.IsNaN(y):
return f64ReturnNaNBinOp(math.Float64bits(x), math.Float64bits(y))
return returnF64NaNBinOp(x, y)
case math.IsInf(x, 1) || math.IsInf(y, 1):
return math.Inf(1)
case x == 0 && x == y:
@@ -135,7 +91,7 @@ func WasmCompatMax32(x, y float32) float32 {
x64, y64 := float64(x), float64(y)
switch {
case math.IsNaN(x64) || math.IsNaN(y64):
return f32ReturnNaNBinOp(math.Float32bits(x), math.Float32bits(y))
return returnF32NaNBinOp(x, y)
case math.IsInf(x64, 1) || math.IsInf(y64, 1):
return float32(math.Inf(1))
case x == 0 && x == y:
@@ -157,10 +113,7 @@ func WasmCompatMax32(x, y float32) float32 {
//
// See https://llvm.org/docs/LangRef.html#llvm-rint-intrinsic.
func WasmCompatNearestF32(f float32) float32 {
if math.IsNaN(float64(f)) {
return f32ReturnNaNUniOp(math.Float32bits(f))
}
var res float32
// TODO: look at https://github.com/bytecodealliance/wasmtime/pull/2171 and reconsider this algorithm
if f != 0 {
ceil := float32(math.Ceil(float64(f)))
@@ -169,14 +122,16 @@ func WasmCompatNearestF32(f float32) float32 {
distToFloor := math.Abs(float64(f - floor))
h := ceil / 2.0
if distToCeil < distToFloor {
f = ceil
res = ceil
} else if distToCeil == distToFloor && float32(math.Floor(float64(h))) == h {
f = ceil
res = ceil
} else {
f = floor
res = floor
}
} else {
res = f
}
return f
return returnF32UniOp(f, res)
}
// WasmCompatNearestF64 is the Wasm spec compatible variant of math.Round, used for Nearest instruction.
@@ -186,11 +141,8 @@ func WasmCompatNearestF32(f float32) float32 {
//
// See https://llvm.org/docs/LangRef.html#llvm-rint-intrinsic.
func WasmCompatNearestF64(f float64) float64 {
if math.IsNaN(f) {
return f64ReturnNaNUniOp(math.Float64bits(f))
}
// TODO: look at https://github.com/bytecodealliance/wasmtime/pull/2171 and reconsider this algorithm
var res float64
if f != 0 {
ceil := math.Ceil(f)
floor := math.Floor(f)
@@ -198,14 +150,16 @@ func WasmCompatNearestF64(f float64) float64 {
distToFloor := math.Abs(f - floor)
h := ceil / 2.0
if distToCeil < distToFloor {
f = ceil
res = ceil
} else if distToCeil == distToFloor && math.Floor(h) == h {
f = ceil
res = ceil
} else {
f = floor
res = floor
}
} else {
res = f
}
return f
return returnF64UniOp(f, res)
}
// WasmCompatCeilF32 is the same as math.Ceil on 32-bit except that
@@ -213,10 +167,7 @@ func WasmCompatNearestF64(f float64) float64 {
// propagation.
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func WasmCompatCeilF32(f float32) float32 {
if math.IsNaN(float64(f)) {
return f32ReturnNaNUniOp(math.Float32bits(f))
}
return float32(math.Ceil(float64(f)))
return returnF32UniOp(f, float32(math.Ceil(float64(f))))
}
// WasmCompatCeilF64 is the same as math.Ceil on 64-bit except that
@@ -224,10 +175,7 @@ func WasmCompatCeilF32(f float32) float32 {
// propagation.
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func WasmCompatCeilF64(f float64) float64 {
if math.IsNaN(f) {
return f64ReturnNaNUniOp(math.Float64bits(f))
}
return math.Ceil(f)
return returnF64UniOp(f, math.Ceil(f))
}
// WasmCompatFloorF32 is the same as math.Floor on 32-bit except that
@@ -235,10 +183,7 @@ func WasmCompatCeilF64(f float64) float64 {
// propagation.
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func WasmCompatFloorF32(f float32) float32 {
if math.IsNaN(float64(f)) {
return f32ReturnNaNUniOp(math.Float32bits(f))
}
return float32(math.Floor(float64(f)))
return returnF32UniOp(f, float32(math.Floor(float64(f))))
}
// WasmCompatFloorF64 is the same as math.Floor on 64-bit except that
@@ -246,10 +191,7 @@ func WasmCompatFloorF32(f float32) float32 {
// propagation.
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func WasmCompatFloorF64(f float64) float64 {
if math.IsNaN(f) {
return f64ReturnNaNUniOp(math.Float64bits(f))
}
return math.Floor(f)
return returnF64UniOp(f, math.Floor(f))
}
// WasmCompatTruncF32 is the same as math.Trunc on 32-bit except that
@@ -257,10 +199,7 @@ func WasmCompatFloorF64(f float64) float64 {
// propagation.
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func WasmCompatTruncF32(f float32) float32 {
if math.IsNaN(float64(f)) {
return f32ReturnNaNUniOp(math.Float32bits(f))
}
return float32(math.Trunc(float64(f)))
return returnF32UniOp(f, float32(math.Trunc(float64(f))))
}
// WasmCompatTruncF64 is the same as math.Trunc on 64-bit except that
@@ -268,8 +207,65 @@ func WasmCompatTruncF32(f float32) float32 {
// propagation.
// https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func WasmCompatTruncF64(f float64) float64 {
if math.IsNaN(f) {
return f64ReturnNaNUniOp(math.Float64bits(f))
}
return math.Trunc(f)
return returnF64UniOp(f, math.Trunc(f))
}
func f32IsNaN(v float32) bool {
return v != v // this is how NaN is defined.
}
func f64IsNaN(v float64) bool {
return v != v // this is how NaN is defined.
}
// returnF32UniOp returns the result of 32-bit unary operation. This accepts `original` which is the operand,
// and `result` which is its result. This returns the `result` as-is if the result is not NaN. Otherwise, this follows
// the same logic as in the reference interpreter as well as the amd64 and arm64 floating point handling.
func returnF32UniOp(original, result float32) float32 {
// Following the same logic as in the reference interpreter:
// https://github.com/WebAssembly/spec/blob/d48af683f5e6d00c13f775ab07d29a15daf92203/interpreter/exec/fxx.ml#L115-L122
if !f32IsNaN(result) {
return result
}
if !f32IsNaN(original) {
return math.Float32frombits(F32CanonicalNaNBits)
}
return math.Float32frombits(math.Float32bits(original) | F32CanonicalNaNBits)
}
// returnF32UniOp returns the result of 64-bit unary operation. This accepts `original` which is the operand,
// and `result` which is its result. This returns the `result` as-is if the result is not NaN. Otherwise, this follows
// the same logic as in the reference interpreter as well as the amd64 and arm64 floating point handling.
func returnF64UniOp(original, result float64) float64 {
// Following the same logic as in the reference interpreter (== amd64 and arm64's behavior):
// https://github.com/WebAssembly/spec/blob/d48af683f5e6d00c13f775ab07d29a15daf92203/interpreter/exec/fxx.ml#L115-L122
if !f64IsNaN(result) {
return result
}
if !f64IsNaN(original) {
return math.Float64frombits(F64CanonicalNaNBits)
}
return math.Float64frombits(math.Float64bits(original) | F64CanonicalNaNBits)
}
// returnF64NaNBinOp returns a NaN for 64-bit binary operations. `x` and `y` are original floats
// and at least one of them is NaN. The returned NaN is guaranteed to comply with the NaN propagation
// procedure: https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func returnF64NaNBinOp(x, y float64) float64 {
if f64IsNaN(x) {
return math.Float64frombits(math.Float64bits(x) | F64CanonicalNaNBits)
} else {
return math.Float64frombits(math.Float64bits(y) | F64CanonicalNaNBits)
}
}
// returnF64NaNBinOp returns a NaN for 32-bit binary operations. `x` and `y` are original floats
// and at least one of them is NaN. The returned NaN is guaranteed to comply with the NaN propagation
// procedure: https://www.w3.org/TR/2022/WD-wasm-core-2-20220419/exec/numerics.html#nan-propagation
func returnF32NaNBinOp(x, y float32) float32 {
if f32IsNaN(x) {
return math.Float32frombits(math.Float32bits(x) | F32CanonicalNaNBits)
} else {
return math.Float32frombits(math.Float32bits(y) | F32CanonicalNaNBits)
}
}

68
internal/moremath/moremath_test.go
View File

@@ -137,3 +137,71 @@ func TestUniOp_NaNPropagation(t *testing.T) {
})
}
}
func Test_returnF32UniOp(t *testing.T) {
for _, tc := range []struct {
original, result, exp uint32
}{
{result: math.Float32bits(1.1), exp: math.Float32bits(1.1)},
{original: 1.0, result: math.Float32bits(float32(math.NaN())), exp: F32CanonicalNaNBits},
{original: F32ArithmeticNaNBits, result: math.Float32bits(float32(math.NaN())), exp: F32ArithmeticNaNBits},
// Even if the MSB of the payload is unset (signaling NaN), the result must it set, therefore an arithmetic NaN.
{original: F32ArithmeticNaNBits ^ (1 << 22), result: math.Float32bits(float32(math.NaN())), exp: F32ArithmeticNaNBits},
} {
actual := returnF32UniOp(math.Float32frombits(tc.original), math.Float32frombits(tc.result))
require.Equal(t, tc.exp, math.Float32bits(actual))
}
}
func Test_returnF64UniOp(t *testing.T) {
for _, tc := range []struct {
original, result, exp uint64
}{
{result: math.Float64bits(1.1), exp: math.Float64bits(1.1)},
{original: 1.0, result: math.Float64bits(math.NaN()), exp: F64CanonicalNaNBits},
{original: F64ArithmeticNaNBits, result: math.Float64bits(math.NaN()), exp: F64ArithmeticNaNBits},
// Even if the MSB of the payload is unset (signaling NaN), the result must it set, therefore an arithmetic NaN.
{original: F64ArithmeticNaNBits ^ (1 << 51), result: math.Float64bits(math.NaN()), exp: F64ArithmeticNaNBits},
} {
actual := returnF64UniOp(math.Float64frombits(tc.original), math.Float64frombits(tc.result))
require.Equal(t, tc.exp, math.Float64bits(actual))
}
}
func Test_returnF32NaNBinOp(t *testing.T) {
for _, tc := range []struct {
x, y, exp uint32
}{
{x: F32CanonicalNaNBits, y: F32CanonicalNaNBits, exp: F32CanonicalNaNBits},
{x: F32CanonicalNaNBits, y: 0, exp: F32CanonicalNaNBits},
{x: 0, y: F32CanonicalNaNBits, exp: F32CanonicalNaNBits},
{x: F32ArithmeticNaNBits, y: F32ArithmeticNaNBits, exp: F32ArithmeticNaNBits},
{x: F32ArithmeticNaNBits, y: 0, exp: F32ArithmeticNaNBits},
{x: 0, y: F32ArithmeticNaNBits, exp: F32ArithmeticNaNBits},
// Even if the MSB of the payload is unset (signaling NaN), the result must it set, therefore an arithmetic NaN.
{x: 0, y: F32ArithmeticNaNBits ^ (1 << 22), exp: F32ArithmeticNaNBits},
{x: F32ArithmeticNaNBits ^ (1 << 22), y: 0, exp: F32ArithmeticNaNBits},
} {
actual := returnF32NaNBinOp(math.Float32frombits(tc.x), math.Float32frombits(tc.y))
require.Equal(t, tc.exp, math.Float32bits(actual))
}
}
func Test_returnF64NaNBinOp(t *testing.T) {
for _, tc := range []struct {
x, y, exp uint64
}{
{x: F64CanonicalNaNBits, y: F64CanonicalNaNBits, exp: F64CanonicalNaNBits},
{x: F64CanonicalNaNBits, y: 0, exp: F64CanonicalNaNBits},
{x: 0, y: F64CanonicalNaNBits, exp: F64CanonicalNaNBits},
{x: F64ArithmeticNaNBits, y: F64ArithmeticNaNBits, exp: F64ArithmeticNaNBits},
{x: F64ArithmeticNaNBits, y: 0, exp: F64ArithmeticNaNBits},
{x: 0, y: F64ArithmeticNaNBits, exp: F64ArithmeticNaNBits},
// Even if the MSB of the payload is unset (signaling NaN), the result must it set, therefore an arithmetic NaN.
{x: 0, y: F64ArithmeticNaNBits ^ (1 << 51), exp: F64ArithmeticNaNBits},
{x: F64ArithmeticNaNBits ^ (1 << 51), y: 0, exp: F64ArithmeticNaNBits},
} {
actual := returnF64NaNBinOp(math.Float64frombits(tc.x), math.Float64frombits(tc.y))
require.Equal(t, tc.exp, math.Float64bits(actual))
}
}