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ec/asm/x25519-x86_64.pl: remove redundant carry chain.

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Why is it redundant? We're looking at carry from addition of small,
11-bit number to 256-bit one. And carry would mean only one thing,
resulting first limb being small number and remaing ones - zeros.
Hence adding 38 to first limb can't carry.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5476)
This commit is contained in:
Andy Polyakov 2018-02-27 19:02:21 +01:00
parent c39e4048b5
commit e72bf96718
1 changed files with 6 additions and 15 deletions
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21
crypto/ec/asm/x25519-x86_64.pl
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@ -40,12 +40,12 @@
# P4 +22% +40%
# Sandy Bridge -3% +11%
# Haswell -1% +13%
# Broadwell(***) +26% +30%
# Skylake(***) +30% +47%
# Broadwell(***) +30% +35%
# Skylake(***) +33% +47%
# Silvermont +20% +26%
# Goldmont +40% +50%
# Bulldozer +20% +9%
# Ryzen(***) +35% +32%
# Ryzen(***) +43% +40%
# VIA +170% +120%
#
# (*) amd64-51 is popular assembly implementation with 2^51 radix,
@ -631,13 +631,10 @@ x25519_fe64_sqr:
and \$38,%rax
add %rax,$acc0
adc \$0,$acc1
mov $acc0,8*0(%rdi)
adc \$0,$acc2
mov $acc1,8*1(%rdi)
adc \$0,$acc3
mov $acc2,8*2(%rdi)
mov $acc3,8*3(%rdi)
mov $acc0,8*0(%rdi)
mov 8*3(%rsp),%r15
mov 8*4(%rsp),%r14
@ -674,13 +671,10 @@ x25519_fe64_mul121666:
and \$38,%rax
add %rax,$acc0
adc \$0,$acc1
mov $acc0,8*0(%rdi)
adc \$0,$acc2
mov $acc1,8*1(%rdi)
adc \$0,$acc3
mov $acc2,8*2(%rdi)
mov $acc3,8*3(%rdi)
mov $acc0,8*0(%rdi)
ret
.size x25519_fe64_mul121666,.-x25519_fe64_mul121666
@ -769,14 +763,11 @@ x25519_fe64_tobytes:
and \$19,%rax
add %rax,$acc0
adc \$0,$acc1
adc \$0,$acc2
adc \$0,$acc3
mov $acc0,8*0(%rdi)
mov $acc1,8*1(%rdi)
mov $acc2,8*2(%rdi)
mov $acc3,8*3(%rdi)
mov $acc0,8*0(%rdi)
ret
.size x25519_fe64_tobytes,.-x25519_fe64_tobytes