On Wed, 5 Aug 2009, Linus Torvalds wrote:
>
> However, right now my biggest profile hit is on this irritating loop:
>
> /* Unroll it? */
> for (t = 16; t <= 79; t++)
> W[t] = SHA_ROL(W[t-3] ^ W[t-8] ^ W[t-14] ^ W[t-16], 1);
>
> and I haven't been able to move _that_ into the other iterations yet.
Oh yes I have.
Here's the patch that gets me sub-28s git-fsck times. In fact, it gives me
sub-27s times. In fact, it's really close to the OpenSSL times.
And all using plain C.
Again - this is all on x86-64. I suspect 32-bit code ends up having
spills due to register pressure. That said, I did get rid of that big
temporary array, and it now basically only uses that 512-bit array as one
circular queue.
Linus
PS. Ok, so my definition of "plain C" is a bit odd. There's nothing plain
about it. It's disgusting C preprocessor misuse. But dang, it's kind of
fun to abuse the compiler this way.
---
block-sha1/sha1.c | 28 ++++++++++++++++------------
1 files changed, 16 insertions(+), 12 deletions(-)
diff --git a/block-sha1/sha1.c b/block-sha1/sha1.c
index 39a5bbb..80193d4 100644
--- a/block-sha1/sha1.c
+++ b/block-sha1/sha1.c
@@ -96,9 +96,8 @@ void blk_SHA1_Final(unsigned char hashout[20], blk_SHA_CTX *ctx)
static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
{
- int t;
unsigned int A,B,C,D,E,TEMP;
- unsigned int W[80];
+ unsigned int array[16];
A = ctx->H[0];
B = ctx->H[1];
@@ -107,8 +106,8 @@ static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
E = ctx->H[4];
#define T_0_15(t) \
- TEMP = htonl(data[t]); W[t] = TEMP; \
- TEMP += SHA_ROL(A,5) + (((C^D)&B)^D) + E + 0x5a827999; \
+ TEMP = htonl(data[t]); array[t] = TEMP; \
+ TEMP += SHA_ROL(A,5) + (((C^D)&B)^D) + E + 0x5a827999; \
E = D; D = C; C = SHA_ROR(B, 2); B = A; A = TEMP; \
T_0_15( 0); T_0_15( 1); T_0_15( 2); T_0_15( 3); T_0_15( 4);
@@ -116,18 +115,21 @@ static void blk_SHA1Block(blk_SHA_CTX *ctx, const unsigned int *data)
T_0_15(10); T_0_15(11); T_0_15(12); T_0_15(13); T_0_15(14);
T_0_15(15);
- /* Unroll it? */
- for (t = 16; t <= 79; t++)
- W[t] = SHA_ROL(W[t-3] ^ W[t-8] ^ W[t-14] ^ W[t-16], 1);
+/* This "rolls" over the 512-bit array */
+#define W(x) (array[(x)&15])
+#define SHA_XOR(t) \
+ TEMP = SHA_ROL(W(t+13) ^ W(t+8) ^ W(t+2) ^ W(t), 1); W(t) = TEMP;
#define T_16_19(t) \
- 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;
+ SHA_XOR(t); \
+ TEMP += SHA_ROL(A,5) + (((C^D)&B)^D) + E + 0x5a827999; \
+ E = D; D = C; C = SHA_ROR(B, 2); B = A; A = TEMP; \
T_16_19(16); T_16_19(17); T_16_19(18); T_16_19(19);
#define T_20_39(t) \
- TEMP = SHA_ROL(A,5) + (B^C^D) + E + W[t] + 0x6ed9eba1; \
+ SHA_XOR(t); \
+ TEMP += SHA_ROL(A,5) + (B^C^D) + E + 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);
@@ -136,7 +138,8 @@ 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_ROL(A,5) + ((B&C)|(D&(B|C))) + E + W[t] + 0x8f1bbcdc; \
+ SHA_XOR(t); \
+ TEMP += SHA_ROL(A,5) + ((B&C)|(D&(B|C))) + E + 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);
@@ -145,7 +148,8 @@ 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_ROL(A,5) + (B^C^D) + E + W[t] + 0xca62c1d6; \
+ SHA_XOR(t); \
+ TEMP += SHA_ROL(A,5) + (B^C^D) + E + 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);
--
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