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Use Assembly cmov on x86

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Mamy André-Ratsimbazafy 2020-02-29 18:27:20 +01:00
parent 309a15ce8b
commit ca817fcb69
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2 changed files with 62 additions and 16 deletions
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8
benchmarks/bls12_381_fp.nim
View File

@ -43,8 +43,8 @@ proc addBench() =
x += y
let stop = getMonotime()
echo &"Time for {Iters} conditional additions (constant-time 381-bit): {inMilliseconds(stop-start)} ms"
echo &"Time for 1 conditional addition ==> {inNanoseconds((stop-start) div Iters)} ns"
echo &"Time for {Iters} additions in 𝔽p (constant-time 381-bit): {inMilliseconds(stop-start)} ms"
echo &"Time for 1 addition in 𝔽p ==> {inNanoseconds((stop-start) div Iters)} ns"
addBench()
@ -60,7 +60,7 @@ proc mulBench() =
r.prod(x, y)
let stop = getMonotime()
echo &"Time for {Iters} multiplications (constant-time 381-bit): {inMilliseconds(stop-start)} ms"
echo &"Time for 1 multiplication ==> {inNanoseconds((stop-start) div Iters)} ns"
echo &"Time for {Iters} multiplications 𝔽p (constant-time 381-bit): {inMilliseconds(stop-start)} ms"
echo &"Time for 1 multiplication 𝔽p ==> {inNanoseconds((stop-start) div Iters)} ns"
mulBench()

70
constantine/primitives/constant_time.nim
View File

@ -227,7 +227,7 @@ template `<=`*[T: Ct](x, y: T): CTBool[T] =
template `xor`*[T: Ct](x, y: CTBool[T]): CTBool[T] =
CTBool[T](noteq(T(x), T(y)))
template mux*[T: Ct](ctl: CTBool[T], x, y: T): T =
func mux*[T](ctl: CTBool[T], x, y: T): T {.inline.}=
## Multiplexer / selector
## Returns x if ctl is true
## else returns y
@ -237,22 +237,68 @@ template mux*[T: Ct](ctl: CTBool[T], x, y: T): T =
# Alternatives:
# - https://cryptocoding.net/index.php/Coding_rules
# - https://www.cl.cam.ac.uk/~rja14/Papers/whatyouc.pdf
#
# TODO: assembly fastpath for conditional mov
let # Templates duplicate input params code
x_Mux = x
y_Mux = y
y_Mux xor (-T(ctl) and (x_Mux xor y_Mux))
when defined(amd64) or defined(i386):
when sizeof(T) == 8:
var muxed = x
asm """
testq %[ctl], %[ctl]
cmovzq %[y], %[muxed]
: [muxed] "+r" (`muxed`)
: [ctl] "r" (`ctl`), [y] "r" (`y`)
: "cc"
"""
muxed
elif sizeof(T) == 4:
var muxed = x
asm """
testl %[ctl], %[ctl]
cmovzl %[y], %[muxed]
: [muxed] "+r" (`muxed`)
: [ctl] "r" (`ctl`), [y] "r" (`y`)
: "cc"
"""
muxed
else:
{.error: "Unsupported word size".}
else:
let # Templates duplicate input params code
x_Mux = x
y_Mux = y
y_Mux xor (-T(ctl) and (x_Mux xor y_Mux))
template mux*[T: CTBool](ctl: CTBool, x, y: T): T =
func mux*[T: CTBool](ctl: CTBool, x, y: T): T {.inline.}=
## Multiplexer / selector
## Returns x if ctl is true
## else returns y
## So equivalent to ctl? x: y
let # Templates duplicate input params code
x_Mux = x
y_Mux = y
T(T.T(y_Mux) xor (-T.T(ctl) and T.T(x_Mux xor y_Mux)))
when defined(amd64) or defined(i386):
when sizeof(T) == 8:
var muxed = x
asm """
testq %[ctl], %[ctl]
cmovzq %[y], %[muxed]
: [muxed] "+r" (`muxed`)
: [ctl] "r" (`ctl`), [y] "r" (`y`)
: "cc"
"""
muxed
elif sizeof(T) == 4:
var muxed = x
asm """
testl %[ctl], %[ctl]
cmovzl %[y], %[muxed]
: [muxed] "+r" (`muxed`)
: [ctl] "r" (`ctl`), [y] "r" (`y`)
: "cc"
"""
muxed
else:
{.error: "Unsupported word size".}
else:
let # Templates duplicate input params code
x_Mux = x
y_Mux = y
T(T.T(y_Mux) xor (-T.T(ctl) and T.T(x_Mux xor y_Mux)))
# ############################################################
#