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Generate smaller code for picking a sign value

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman 2023-08-09 18:55:41 +01:00
parent 444d1e7608
commit f3df105b37
1 changed files with 9 additions and 5 deletions
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14
library/bignum.c
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@ -258,6 +258,10 @@ static inline mbedtls_mpi_uint mpi_sint_abs(mbedtls_mpi_sint z)
return (mbedtls_mpi_uint) 0 - (mbedtls_mpi_uint) z;
}
/* Convert x to a sign, i.e. to 1, if x is positive, or -1, if x is negative.
* This looks awkward but generates smaller code than (x < 0 ? -1 : 1) */
#define TO_SIGN(x) ((((mbedtls_mpi_uint)x) >> (biL - 1)) * -2 + 1)
/*
* Set value from integer
*/
@ -270,7 +274,7 @@ int mbedtls_mpi_lset(mbedtls_mpi *X, mbedtls_mpi_sint z)
memset(X->p, 0, X->n * ciL);
X->p[0] = mpi_sint_abs(z);
X->s = (z < 0) ? -1 : 1;
X->s = TO_SIGN(z);
cleanup:
@ -880,7 +884,7 @@ int mbedtls_mpi_cmp_int(const mbedtls_mpi *X, mbedtls_mpi_sint z)
MPI_VALIDATE_RET(X != NULL);
*p = mpi_sint_abs(z);
Y.s = (z < 0) ? -1 : 1;
Y.s = TO_SIGN(z);
Y.n = 1;
Y.p = p;
@ -1068,7 +1072,7 @@ int mbedtls_mpi_add_int(mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_sint b
MPI_VALIDATE_RET(A != NULL);
p[0] = mpi_sint_abs(b);
B.s = (b < 0) ? -1 : 1;
B.s = TO_SIGN(b);
B.n = 1;
B.p = p;
@ -1086,7 +1090,7 @@ int mbedtls_mpi_sub_int(mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_sint b
MPI_VALIDATE_RET(A != NULL);
p[0] = mpi_sint_abs(b);
B.s = (b < 0) ? -1 : 1;
B.s = TO_SIGN(b);
B.n = 1;
B.p = p;
@ -1436,7 +1440,7 @@ int mbedtls_mpi_div_int(mbedtls_mpi *Q, mbedtls_mpi *R,
MPI_VALIDATE_RET(A != NULL);
p[0] = mpi_sint_abs(b);
B.s = (b < 0) ? -1 : 1;
B.s = TO_SIGN(b);
B.n = 1;
B.p = p;