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Fix shift by bytes/bit in multiplication (need tests)

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mratsim 2018-02-16 13:54:03 +01:00
parent 71d1f5bd19
commit cec8a752fb
1 changed files with 4 additions and 2 deletions
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6
src/uint_binary_ops.nim
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@ -77,7 +77,9 @@ template naiveMulImpl[T: MpUint](x, y: T): MpUint[T] =
# and introduce branching
# - More total operations means more register moves
const halfShl = T.sizeof div 2
let # TODO: should be a const - https://github.com/nim-lang/Nim/pull/5664
size = (T.sizeof * 8)
halfSize = size div 2
let
z0 = naiveMul(x.lo, y.lo)
tmp = naiveMul(x.hi, y.lo)
@ -86,7 +88,7 @@ template naiveMulImpl[T: MpUint](x, y: T): MpUint[T] =
z1 += naiveMul(x.hi, y.lo)
let z2 = (z1 < tmp).T + naiveMul(x.hi, y.hi)
result.lo = z1.lo shl halfShl + z0
result.lo = z1.lo shl halfSize + z0
result.hi = z2 + z1.hi
proc naiveMul[T: BaseUint](x, y: T): MpUint[T] {.noSideEffect, noInit, inline.}=