[PATCH 4/5] crypto/sha1.c: avoid successively shifting a long long
Shifting a long long about 7 times to store the length bits is suboptimal
on most 32-bit architectures. Use a 32 bit scratch instead.
This provides an appreciable code reduction considering the _whole_
of the sha1_final() function:
arch old size new size reduction
---------------------------------------------------------
i386 0xe0 0xc4 12.5%
arm 0x15c 0xe8 33.3%
Smaller code in this case is of course faster code.
Signed-off-by: Nicolas Pitre <[email protected]>
Index: linux-2.6/crypto/sha1.c
===================================================================
--- linux-2.6.orig/crypto/sha1.c
+++ linux-2.6/crypto/sha1.c
@@ -75,8 +75,8 @@
static void sha1_final(void* ctx, u8 *out)
{
struct sha1_ctx *sctx = ctx;
- u32 i, j, index, padlen;
- u64 t, count = sctx->count;
+ u64 count = sctx->count;
+ u32 i, j, index, padlen, t;
u8 bits[8];
static const u8 padding[64] = { 0x80, };
@@ -90,7 +90,8 @@
bits[7] = 0xff & t; t>>=8;
bits[6] = 0xff & t; t>>=8;
bits[5] = 0xff & t; t>>=8;
- bits[4] = 0xff & t; t>>=8;
+ bits[4] = 0xff & t;
+ t = count >> (32 - 3);
bits[3] = 0xff & t; t>>=8;
bits[2] = 0xff & t; t>>=8;
bits[1] = 0xff & t; t>>=8;
-
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