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perpare for more compact bit operations in JS #16728

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Jan 19, 2021
Merged

perpare for more compact bit operations in JS #16728

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15 changes: 8 additions & 7 deletions lib/pure/math.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -159,14 +159,15 @@ func isNaN*(x: SomeFloat): bool {.inline, since: (1,5,1).} =
else: result = c_isnan(x)

when defined(js):
import std/private/jsutils

proc toBitsImpl(x: float): array[2, uint32] =
asm """
const buffer = new ArrayBuffer(8);
const floatBuffer = new Float64Array(buffer);
const uintBuffer = new Uint32Array(buffer);
floatBuffer[0] = `x`;
`result` = uintBuffer
"""
let buffer = newArrayBuffer(8)
let floatBuffer = newFloat64Array(buffer)
let uintBuffer = newUint32Array(buffer)
floatBuffer[0] = x
{.emit: "`result` = `uintBuffer`;".}
# result = cast[array[2, uint32]](uintBuffer)
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proc signbit*(x: SomeFloat): bool {.inline, since: (1, 5, 1).} =
## Returns true if `x` is negative, false otherwise.
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12 changes: 12 additions & 0 deletions lib/std/private/jsutils.nim
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
when defined(js):
type
ArrayBuffer* = ref object of JsRoot
Float64Array* = ref object of JsRoot
Uint32Array* = ref object of JsRoot

func newArrayBuffer*(n: int): ArrayBuffer {.importjs: "new ArrayBuffer(#)".}
func newFloat64Array*(buffer: ArrayBuffer): Float64Array {.importjs: "new Float64Array(#)".}
func newUint32Array*(buffer: ArrayBuffer): Uint32Array {.importjs: "new Uint32Array(#)".}

func `[]`*(arr: Uint32Array, i: int): uint32 {.importjs: "#[#]".}
func `[]=`*(arr: Float64Array, i: int, v: float) {.importjs: "#[#] = #".}
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@timotheecour timotheecour Jan 15, 2021 •
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should this be arr: Float64Array or arr: var Float64Array ? I'm really not sure here since the type is ref, but really, Float64Array + friends act like seq, so var seems to make more sense here.

what are downsides of using var here?

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var will generates array of typed array

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yes, this is generally true of var in nim js; the question is whether this has a performance impact in this case or whether v8 can optimize this (I'm not sure how to check other than performance timing)

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@ringabout ringabout Jan 29, 2021 •
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It seems to cause some errors in some situations, but I forgot the example.

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note that for var you need the awkard syntax like this: [#][0][0]

# eg: jsbigints:
func inc*(this: var JsBigInt; amount: JsBigInt) {.importjs: "([#][0][0] += #)".} =

(until nim-lang/RFCs#315 is resolved)