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lib/mpi: mpi_read_buffer(): optimize skipping of leading zero limbs 

Currently, if the number of leading zeros is greater than fits into a
complete limb, mpi_read_buffer() skips them by iterating over them
limb-wise.

Instead of skipping the high order zero limbs within the loop as shown
above, adjust the copying loop's bounds.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Nicolai Stange 2016-03-22 13:12:40 +01:00 committed by Herbert Xu
parent d755290689
commit f00fa2417b
1 changed files with 8 additions and 10 deletions
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18
lib/mpi/mpicoder.c
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@ -184,7 +184,9 @@ int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
p = buf;
*nbytes = n - lzeros;
for (i = a->nlimbs - 1; i >= 0; i--) {
for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
lzeros %= BYTES_PER_MPI_LIMB;
i >= 0; i--) {
alimb = a->d[i];
#if BYTES_PER_MPI_LIMB == 4
*p++ = alimb >> 24;
@ -205,15 +207,11 @@ int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
#endif
if (lzeros > 0) {
if (lzeros >= sizeof(alimb)) {
p -= sizeof(alimb);
} else {
mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
+ lzeros;
*limb1 = *limb2;
p -= lzeros;
}
mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
+ lzeros;
*limb1 = *limb2;
p -= lzeros;
lzeros -= sizeof(alimb);
}
}