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make copySign for js consistent with other backends (#16609)

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* make copySign work more robustly in js
* improve tests
* improve tests/vm/tcastint.nim
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Timothee Cour 2021-02-21 23:47:00 -08:00 • committed by GitHub
commit cde950e1bc
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3 changed files with 48 additions and 44 deletions
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45
lib/pure/math.nim
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@ -175,11 +175,24 @@ when defined(js):
proc toBitsImpl(x: float): array[2, uint32] =
let buffer = newArrayBuffer(8)
let floatBuffer = newFloat64Array(buffer)
let uintBuffer = newUint32Array(buffer)
floatBuffer[0] = x
{.emit: "`result` = `uintBuffer`;".}
# result = cast[array[2, uint32]](uintBuffer)
let a = newFloat64Array(buffer)
let b = newUint32Array(buffer)
a[0] = x
{.emit: "`result` = `b`;".}
# result = cast[array[2, uint32]](b)
proc jsSetSign(x: float, sgn: bool): float =
let buffer = newArrayBuffer(8)
let a = newFloat64Array(buffer)
let b = newUint32Array(buffer)
a[0] = x
asm """
function updateBit(num, bitPos, bitVal) {
return (num & ~(1 << bitPos)) | (bitVal << bitPos);
}
`b`[1] = updateBit(`b`[1], 31, `sgn`);
`result` = `a`[0]
"""
proc signbit*(x: SomeFloat): bool {.inline, since: (1, 5, 1).} =
## Returns true if `x` is negative, false otherwise.
@ -203,19 +216,21 @@ func copySign*[T: SomeFloat](x, y: T): T {.inline, since: (1, 5, 1).} =
doAssert copySign(10.0, -1.0) == -10.0
doAssert copySign(-Inf, -0.0) == -Inf
doAssert copySign(NaN, 1.0).isNaN
doAssert copySign(1.0, copySign(NaN, -1.0)) == -1.0
# TODO: use signbit for examples
template impl() =
if y > 0.0 or (y == 0.0 and 1.0 / y > 0.0):
result = abs(x)
elif y <= 0.0:
result = -abs(x)
else: # must be NaN
result = abs(x)
when defined(js): impl()
when defined(js):
let uintBuffer = toBitsImpl(y)
let sgn = (uintBuffer[1] shr 31) != 0
result = jsSetSign(x, sgn)
else:
when nimvm: impl()
when nimvm: # not exact but we have a vmops for recent enough nim
if y > 0.0 or (y == 0.0 and 1.0 / y > 0.0):
result = abs(x)
elif y <= 0.0:
result = -abs(x)
else: # must be NaN
result = abs(x)
else: result = c_copysign(x, y)
func classify*(x: float): FloatClass =