94 lines
3.0 KiB
Nim
94 lines
3.0 KiB
Nim
# Stint
|
|
# Copyright 2018-Present Status Research & Development GmbH
|
|
# Licensed under either of
|
|
#
|
|
# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
|
|
# * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
|
|
#
|
|
# at your option. This file may not be copied, modified, or distributed except according to those terms.
|
|
|
|
import
|
|
./datatypes
|
|
|
|
# Shifts
|
|
# --------------------------------------------------------
|
|
{.push raises: [], gcsafe.}
|
|
|
|
func shrSmall*(r: var Limbs, a: Limbs, k: SomeInteger) =
|
|
## 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 ..< a.len-1:
|
|
r[i] = (a[i] shr k) or (a[i+1] shl (WordBitWidth - k))
|
|
r[^1] = a[^1] shr k
|
|
else:
|
|
for i in countdown(a.len-1, 1):
|
|
r[i] = (a[i] shr k) or (a[i-1] shl (WordBitWidth - k))
|
|
r[0] = a[0] shr k
|
|
|
|
func shrLarge*(r: var Limbs, a: Limbs, w, shift: SomeInteger) =
|
|
## Shift right by `w` words + `shift` bits
|
|
## Assumes `r` is 0 initialized
|
|
if w > Limbs.len:
|
|
return
|
|
|
|
when cpuEndian == littleEndian:
|
|
for i in w ..< a.len-1:
|
|
r[i-w] = (a[i] shr shift) or (a[i+1] shl (WordBitWidth - shift))
|
|
r[^(1+w)] = a[^1] shr shift
|
|
else:
|
|
for i in countdown(a.len-1, 1+w):
|
|
r[i-w] = (a[i] shr shift) or (a[i-1] shl (WordBitWidth - k))
|
|
r[0] = a[w] shr shift
|
|
|
|
func shrWords*(r: var Limbs, a: Limbs, w: SomeInteger) =
|
|
## Shift right by w word
|
|
when cpuEndian == littleEndian:
|
|
for i in 0 ..< Limbs.len-w:
|
|
r[i] = a[i+w]
|
|
else:
|
|
for i in countdown(Limbs.len-w, 0):
|
|
r[i] = a[i+w]
|
|
|
|
func shlSmall*(r: var Limbs, a: Limbs, k: SomeInteger) =
|
|
## Compute the `shift left` operation of x and k
|
|
##
|
|
## k MUST be less than the base word size (2^32 or 2^64)
|
|
when cpuEndian == littleEndian:
|
|
r[0] = a[0] shl k
|
|
for i in 1 ..< a.len:
|
|
r[i] = (a[i] shl k) or (a[i-1] shr (WordBitWidth - k))
|
|
else:
|
|
r[^1] = a[^1] shl k
|
|
for i in countdown(a.len-2, 0):
|
|
r[i] = (a[i] shl k) or (a[i+1] shr (WordBitWidth - k))
|
|
|
|
func shlLarge*(r: var Limbs, a: Limbs, w, shift: SomeInteger) =
|
|
## Shift left by `w` words + `shift` bits
|
|
## Assumes `r` is 0 initialized
|
|
if w > Limbs.len:
|
|
return
|
|
|
|
when cpuEndian == littleEndian:
|
|
r[w] = a[0] shl shift
|
|
for i in 1+w ..< r.len:
|
|
r[i] = (a[i-w] shl shift) or (a[i-w-1] shr (WordBitWidth - shift))
|
|
else:
|
|
r[^1] = a[^w] shl shift
|
|
for i in countdown(a.len-2-w, 0):
|
|
r[i+w] = (a[i] shl shift) or (a[i+1] shr (WordBitWidth - shift))
|
|
|
|
func shlWords*(r: var Limbs, a: Limbs, w: SomeInteger) =
|
|
## Shift left by w word
|
|
when cpuEndian == littleEndian:
|
|
for i in 0 ..< Limbs.len-w:
|
|
r[i+w] = a[i]
|
|
else:
|
|
for i in countdown(Limbs.len-1, 0):
|
|
r[i] = a[i-w]
|