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Use separate counters for 8-fold and single multiplication steps

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Compilers are likely to generate shorter assembly for loops of the
form `while( cnt-- ) { ... }` rather than
`for( ; count >= X; count -= X ) { ... }`. (E.g. the latter needs
a subtract+compare+branch after each loop, while the former only
needs decrement+branch).

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit is contained in:
Hanno Becker 2022-04-06 11:30:51 +01:00
parent eacf3b9eb4
commit 63eb28c728
1 changed files with 5 additions and 2 deletions
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7
library/bignum.c
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@ -1377,14 +1377,17 @@ mbedtls_mpi_uint mbedtls_mpi_core_mla( mbedtls_mpi_uint *d, size_t d_len,
mbedtls_mpi_uint c = 0; /* carry */
size_t excess_len = d_len - s_len;
for( ; s_len >= 8; s_len -= 8 )
size_t steps_x8 = s_len / 8;
size_t steps_x1 = s_len & 7;
while( steps_x8-- )
{
MULADDC_X8_INIT
MULADDC_X8_CORE
MULADDC_X8_STOP
}
for( ; s_len > 0; s_len-- )
while( steps_x1-- )
{
MULADDC_X1_INIT
MULADDC_X1_CORE