Commit 4e268816 authored by Niels Möller's avatar Niels Möller

(gcm_rightshift): Complete rewrite, to use word rather

than byte operations. Improves gmac performance from 830 cycles /
byte to (still poor) 268 cycles per byte on intel x86_64.

Rev: nettle/gcm.c:1.2
parent 94361563
......@@ -48,22 +48,50 @@
#include "nettle-internal.h"
#include "macros.h"
/* The gcm_rightshift and gcm_gf_mul was copied from
* libtomcrypt, which is under public domain.
* Written by Tom S. Dennis.
*/
/* FIXME: Change representation so we can to word-sized shifts? */
/* Big-endian shift right. The argument must be properly aligned for
word accesses. */
static void
gcm_rightshift (uint8_t * a)
gcm_rightshift (uint8_t *a)
{
int x;
for (x = 15; x > 0; x--)
{
a[x] = (a[x] >> 1) | ((a[x - 1] << 7) & 0x80);
}
a[0] >>= 1;
unsigned long *w = (unsigned long *) a;
/* Shift uses big-endian representation. */
#if WORDS_BIGENDIAN
# if SIZEOF_LONG == 4
w[3] = (w[3] >> 1) | ((w[2] & 1) << 31);
w[2] = (w[2] >> 1) | ((w[1] & 1) << 31);
w[1] = (w[1] >> 1) | ((w[0] & 1) << 31);
w[0] = (w[0] >> 1);
# elif SIZEOF_LONG == 8
w[1] = (w[1] >> 1) | ((w[0] & 1) << 63);
w[0] = (w[0] >> 1);
# else
# error Unsupported word size. */
#endif
#else /* ! WORDS_BIGENDIAN */
# if SIZEOF_LONG == 4
#define RSHIFT_WORD(x) \
((((x) & 0xfefefefeUL) >> 1) \
| (((x) & 0x01010101) << 15))
w[3] = RSHIFT_WORD(w[3]) | ((w[2] >> 17) & 0x80);
w[2] = RSHIFT_WORD(w[2]) | ((w[1] >> 17) & 0x80);
w[1] = RSHIFT_WORD(w[1]) | ((w[0] >> 17) & 0x80);
w[0] = RSHIFT_WORD(w[0]);
# elif SIZEOF_LONG == 8
#define RSHIFT_WORD(x) \
((((x) & 0xfefefefefefefefeUL) >> 1) \
| (((x) & 0x0101010101010101UL) << 15))
w[1] = RSHIFT_WORD(w[1]) | ((w[0] >> 49) & 0x80);
w[0] = RSHIFT_WORD(w[0]);
# else
# error Unsupported word size. */
# endif
#endif /* ! WORDS_BIGENDIAN */
}
/* The function gcm_gf_mul was copied from
* libtomcrypt, which is under public domain.
* Written by Tom S. Dennis.
*/
/**
GCM GF multiplier (internal use only) bitserial
......
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