On Wed, 5 Aug 2009, Nicolas Pitre wrote:
>
> Even better is to not shift len at all in SHA_update() but shift
> ctx->size only at the end in SHA_final(). It is not like if
> SHA_update() could operate on partial bytes, so counting total bytes
> instead of total bits is all you need. This way you need no cast there
> and make the code slightly faster.
Yeah, I tried it, but it's not noticeable.
The bigger issue seems to be that it's shifter-limited, or that's what I
take away from my profiles. I suspect it's even _more_ shifter-limited on
some other micro-architectures, because gcc is being stupid, and generates
ror $31,%eax
from the "left shift + right shift" combination. It seems to -always-
generate a "ror", rather than trying to generate 'rot' if the shift count
would be smaller that way.
And I know _some_ old micro-architectures will literally internally loop
on the rol/ror counts, so "ror $31" can be _much_ more expensive than "rol
$1".
That isn't the case on my Nehalem, though. But I can't seem to get gcc to
generate better code without actually using inline asm..
(So to clarify: this patch makes no difference that I can see to
performance, but I suspect it could matter on other CPU's like an old
Pentium or maybe an Atom).
Linus
---
block-sha1/sha1.c | 36 ++++++++++++++++++++++++------------
block-sha1/sha1.h | 2 +-
2 files changed, 25 insertions(+), 13 deletions(-)
diff --git a/block-sha1/sha1.c b/block-sha1/sha1.c
index 8fd90b0..a45a3de 100644
--- a/block-sha1/sha1.c
+++ b/block-sha1/sha1.c
@@ -80,7 +80,19 @@ void blk_SHA1_Final(unsigned char hashout[20], blk_SHA_CTX *ctx)
((unsigned int *)hashout)[i] = htonl(ctx->H[i]);
}
-#define SHA_ROT(X,n) (((X) << (n)) | ((X) >> (32-(n))))
+#if defined(__i386__) || defined(__x86_64__)
+
+#define SHA_ASM(op, x, n) ({ unsigned int __res; asm(op " %1,%0":"=r" (__res):"i" (n), "0" (x)); __res; })
+#define SHA_ROL(x,n) SHA_ASM("rol", x, n)
+#define SHA_ROR(x,n) SHA_ASM("ror", x, n)
+
+#else
+
+#define SHA_ROT(X,n) (((X) << (l)) | ((X) >> (r)))
+#define SHA_ROL(X,n) SHA_ROT(X,n,32-(n))
+#define SHA_ROR(X,n) SHA_ROT(X,32-(n),n)
+
+#endif
static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
{
@@ -93,7 +105,7 @@ static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
/* Unroll it? */
for (t = 16; t <= 79; t++)
- W[t] = SHA_ROT(W[t-3] ^ W[t-8] ^ W[t-14] ^ W[t-16], 1);
+ W[t] = SHA_ROL(W[t-3] ^ W[t-8] ^ W[t-14] ^ W[t-16], 1);
A = ctx->H[0];
B = ctx->H[1];
@@ -102,8 +114,8 @@ static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
E = ctx->H[4];
#define T_0_19(t) \
- TEMP = SHA_ROT(A,5) + (((C^D)&B)^D) + E + W[t] + 0x5a827999; \
- E = D; D = C; C = SHA_ROT(B, 30); B = A; A = TEMP;
+ TEMP = SHA_ROL(A,5) + (((C^D)&B)^D) + E + W[t] + 0x5a827999; \
+ E = D; D = C; C = SHA_ROR(B, 2); B = A; A = TEMP;
T_0_19( 0); T_0_19( 1); T_0_19( 2); T_0_19( 3); T_0_19( 4);
T_0_19( 5); T_0_19( 6); T_0_19( 7); T_0_19( 8); T_0_19( 9);
@@ -111,8 +123,8 @@ static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
T_0_19(15); T_0_19(16); T_0_19(17); T_0_19(18); T_0_19(19);
#define T_20_39(t) \
- TEMP = SHA_ROT(A,5) + (B^C^D) + E + W[t] + 0x6ed9eba1; \
- E = D; D = C; C = SHA_ROT(B, 30); B = A; A = TEMP;
+ TEMP = SHA_ROL(A,5) + (B^C^D) + E + W[t] + 0x6ed9eba1; \
+ E = D; D = C; C = SHA_ROR(B, 2); B = A; A = TEMP;
T_20_39(20); T_20_39(21); T_20_39(22); T_20_39(23); T_20_39(24);
T_20_39(25); T_20_39(26); T_20_39(27); T_20_39(28); T_20_39(29);
@@ -120,8 +132,8 @@ static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
T_20_39(35); T_20_39(36); T_20_39(37); T_20_39(38); T_20_39(39);
#define T_40_59(t) \
- TEMP = SHA_ROT(A,5) + ((B&C)|(D&(B|C))) + E + W[t] + 0x8f1bbcdc; \
- E = D; D = C; C = SHA_ROT(B, 30); B = A; A = TEMP;
+ TEMP = SHA_ROL(A,5) + ((B&C)|(D&(B|C))) + E + W[t] + 0x8f1bbcdc; \
+ E = D; D = C; C = SHA_ROR(B, 2); B = A; A = TEMP;
T_40_59(40); T_40_59(41); T_40_59(42); T_40_59(43); T_40_59(44);
T_40_59(45); T_40_59(46); T_40_59(47); T_40_59(48); T_40_59(49);
@@ -129,8 +141,8 @@ static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
T_40_59(55); T_40_59(56); T_40_59(57); T_40_59(58); T_40_59(59);
#define T_60_79(t) \
- TEMP = SHA_ROT(A,5) + (B^C^D) + E + W[t] + 0xca62c1d6; \
- E = D; D = C; C = SHA_ROT(B, 30); B = A; A = TEMP;
+ TEMP = SHA_ROL(A,5) + (B^C^D) + E + W[t] + 0xca62c1d6; \
+ E = D; D = C; C = SHA_ROR(B, 2); B = A; A = TEMP;
T_60_79(60); T_60_79(61); T_60_79(62); T_60_79(63); T_60_79(64);
T_60_79(65); T_60_79(66); T_60_79(67); T_60_79(68); T_60_79(69);
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