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15757557b4
* add metering to modexp * modexp: accel exponent = 1 * modexp: improve runtime Montgomery constants compute. 2.49x faster on DOS vectors
48 lines
1.6 KiB
Nim
48 lines
1.6 KiB
Nim
# Constantine
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# Copyright (c) 2018-2019 Status Research & Development GmbH
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# Copyright (c) 2020-Present Mamy André-Ratsimbazafy
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# Licensed and distributed under either of
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# * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
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# * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
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# at your option. This file may not be copied, modified, or distributed except according to those terms.
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import
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# Internal
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../../platforms/abstractions,
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./limbs_multiprec
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# ############################################################
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#
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# Multi-precision modular arithmetic
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#
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# ############################################################
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func addmod_vartime*(r: var openArray[SecretWord], a, b, M: openArray[SecretWord]) {.meter.} =
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## r <- a+b (mod M)
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## assumes a and b are in the range [0, M)
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debug:
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doAssert r.len == M.len
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var tBuf = allocStackArray(SecretWord, r.len)
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template t: untyped = tBuf.toOpenArray(0, r.len-1)
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let overflow = t.addMP(a, b)
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if overflow:
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# t <- a+b overflowed so it is greater than M.
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discard r.subMP(t, M)
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return
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# Operation didn't overflow in an extra limb but r can still be greater than M
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let underflow = r.subMP(t, M)
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# r <- t-M
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# If there is an underflow t < M, t has the correct result
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# if there isn't an underflow, t >= M, r has the correct result
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if underflow:
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for i in 0 ..< r.len:
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r[i] = t[i]
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func doublemod_vartime*(r: var openArray[SecretWord], a, M: openArray[SecretWord]) {.inline, meter.} =
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## r <- 2a (mod M)
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r.addmod_vartime(a, a, M) |