reimplement bitwise

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Mamy André-Ratsimbazafy 2020-06-12 19:23:03 +02:00 committed by jangko
parent 36cc2b2e02
commit cbbffe4e9c
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2 changed files with 47 additions and 42 deletions

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@ -16,7 +16,7 @@ when sizeof(int) == 8 and not defined(Stint32):
else:
type Word* = uint32
const WordBitWidth = sizeof(Word) * 8
const WordBitWidth* = sizeof(Word) * 8
func wordsRequired*(bits: int): int {.compileTime.} =
## Compute the number of limbs required
@ -96,3 +96,12 @@ iterator leastToMostSig*(aLimbs: var Limbs, bLimbs: Limbs): (var Word, Word) =
else:
for i in countdown(limbs.len-1, 0):
yield (aLimbs[i], bLimbs[i])
iterator leastToMostSig*(cLimbs: var Limbs, aLimbs: Limbs, bLimbs: Limbs): (var Word, Word, Word) =
## Iterate from least to most significant word
when cpuEndian == littleEndian:
for i in 0 ..< limbs.len:
yield (cLimbs[i], aLimbs[i], bLimbs[i])
else:
for i in countdown(limbs.len-1, 0):
yield (cLimbs[i], aLimbs[i], bLimbs[i])

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@ -7,56 +7,52 @@
#
# at your option. This file may not be copied, modified, or distributed except according to those terms.
import ./datatypes, ./bitops2_priv
import ./datatypes
func `not`*(x: UintImpl): UintImpl {.inline.}=
func `not`*(x: Limbs): Limbs {.inline.}=
## Bitwise complement of unsigned integer x
applyHiLo(x, `not`)
for wr, wx in leastToMostSig(result, x):
wr = not wx
func `or`*(x, y: UintImpl): UintImpl {.inline.}=
func `or`*(x, y: Limbs): Limbs {.inline.}=
## `Bitwise or` of numbers x and y
applyHiLo(x, y, `or`)
for wr, wx, wy in leastToMostSig(result, x, y):
wr = wx or wy
func `and`*(x, y: UintImpl): UintImpl {.inline.}=
func `and`*(x, y: Limbs): Limbs {.inline.}=
## `Bitwise and` of numbers x and y
applyHiLo(x, y, `and`)
for wr, wx, wy in leastToMostSig(result, x, y):
wr = wx and wy
func `xor`*(x, y: UintImpl): UintImpl {.inline.}=
func `xor`*(x, y: Limbs): Limbs {.inline.}=
## `Bitwise xor` of numbers x and y
applyHiLo(x, y, `xor`)
for wr, wx, wy in leastToMostSig(result, x, y):
wr = wx xor wy
func `shr`*(x: UintImpl, y: SomeInteger): UintImpl {.inline.}
# Forward declaration
func `shl`*(x: UintImpl, y: SomeInteger): UintImpl {.inline.}=
## Compute the `shift left` operation of x and y
# Note: inlining this poses codegen/aliasing issue when doing `x = x shl 1`
# TODO: would it be better to reimplement this with words iteration?
const halfSize: type(y) = bitsof(x) div 2
if y == 0:
return x
elif y == halfSize:
result.hi = x.lo
elif y < halfSize:
result.hi = (x.hi shl y) or (x.lo shr (halfSize - y))
result.lo = x.lo shl y
func `shr`*(x: Limbs, k: SomeInteger): Limbs {.inline.} =
## Shift right by k.
##
## k MUST be less than the base word size (2^32 or 2^64)
# Note: for speed, loading a[i] and a[i+1]
# instead of a[i-1] and a[i]
# is probably easier to parallelize for the compiler
# (antidependence WAR vs loop-carried dependence RAW)
when cpuEndian == littleEndian:
for i in 0 ..< x.len-1:
result[i] = (x[i] shr k) or (x[i+1] shl (WordBitWidth - k))
result[^1] = x[^1] shr k
else:
result.hi = x.lo shl (y - halfSize)
for i in countdown(x.len-1, 1):
result[i] = (x[i] shr k) or (x[i-1] shl (WordBitWidth - k))
result[0] = x[0] shr k
func `shr`*(x: UintImpl, y: SomeInteger): UintImpl {.inline.}=
## Compute the `shift right` operation of x and y
## Similar to C standard, result is undefined if y is bigger
## than the number of bits in x.
const halfSize: type(y) = bitsof(x) div 2
if y == 0:
return x
elif y == halfSize:
result.lo = x.hi
elif y < halfSize:
result.lo = (x.lo shr y) or (x.hi shl (halfSize - y))
result.hi = x.hi shr y
func `shl`*(x: Limbs, k: SomeInteger): Limbs {.inline.}=
## Compute the `shift left` operation of x and k
when cpuEndian == littleEndian:
result[0] = x[0] shl k
for i in 1 ..< x.len:
result[i] = (x[i] shl k) or (x[i-1] shr (WordBitWidth - k))
else:
result.lo = x.hi shr (y - halfSize)
result[^1] = x[^1] shl k
for i in countdown(x.len-2, 0):
result[i] = (x[i] shl k) or (x[i+1] shr (WordBitWidth - k))