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manually do 128 bit multiplication to avoid bitshift and fix wasm tests

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Brendan Hansknecht 2022-12-02 15:17:52 -08:00
parent 436bfc41ed
commit ab6c652360
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1 changed files with 25 additions and 3 deletions
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crates/compiler/builtins/roc/Dict.roc
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@ -986,10 +986,32 @@ wymix = \a, b ->
wymum : U64, U64 -> { lower : U64, upper : U64 }
wymum = \a, b ->
r = Num.toU128 a * Num.toU128 b
lower = Num.toU64 r
upper = Num.shiftRightZfBy r 64 |> Num.toU64
# uint64_t ha=*A>>32, hb=*B>>32, la=(uint32_t)*A, lb=(uint32_t)*B, hi, lo;
# uint64_t rh=ha*hb, rm0=ha*lb, rm1=hb*la, rl=la*lb, t=rl+(rm0<<32), c=t<rl;
# lo=t+(rm1<<32); c+=lo<t; hi=rh+(rm0>>32)+(rm1>>32)+c;
ha = Num.shiftRightZfBy a 32
hb = Num.shiftRightZfBy b 32
la = Num.bitwiseAnd a 0x0000_0000_FFFF_FFFF
lb = Num.bitwiseAnd b 0x0000_0000_FFFF_FFFF
rh = ha * hb
rm0 = ha * lb
rm1 = hb * la
rl = la * lb
t = Num.addWrap rl (Num.shiftLeftBy rm0 32)
c = if t < rl then 1 else 0
lower = Num.addWrap t (Num.shiftLeftBy rm1 32)
c2 = c + (if lower < t then 1 else 0)
upper =
rh
|> Num.addWrap (Num.shiftRightZfBy rm0 32)
|> Num.addWrap (Num.shiftRightZfBy rm1 32)
|> Num.addWrap c2
# TODO: switch back to this once wasm supports bit shifting a U128.
# The above code is manually doing the 128bit multiplication.
# r = Num.toU128 a * Num.toU128 b
# lower = Num.toU64 r
# upper = Num.shiftRightZfBy r 64 |> Num.toU64
# This is the more robust form.
# { lower: Num.bitwiseXor a lower, upper: Num.bitwiseXor b upper }
{ lower, upper }