diff options
author | Alois Klink <alois@aloisklink.com> | 2023-04-16 15:40:01 +0100 |
---|---|---|
committer | Alois Klink <alois@aloisklink.com> | 2023-04-16 16:45:21 +0100 |
commit | 326af4ad171b849ba1e76fd425d8f337718c4108 (patch) | |
tree | 6b53a6c13812e1a1a6c3539811088498a3a35728 /crypto/bn | |
parent | 8835940db58229fc467cdea1eebf3f064352a086 (diff) |
bn_nist: replace pointer bit-fiddling with ternary
Bit-fiddling pointers is technically implementation defined behavior
in the C specification so the following code is not supported in all
platforms:
PTR_SIZE_INT mask;
void * a, b, c;
int boolean_flag;
mask = 0 - boolean_flag;
/* Not guaranteed to be a valid ptr to a or b on all platforms */
a = (void *)
((((PTR_SIZE_INT) b & ~mask) | (((PTR_SIZE_INT)) c & mask)));
Using a ternary conditional operator is supported on all platforms
(i.e. `a = boolean_flag ? b : c;`).
On most modern compilers/CPUs, this will be faster, since it will
get converted to a CMOV instruction.
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20748)
Diffstat (limited to 'crypto/bn')
-rw-r--r-- | crypto/bn/bn_nist.c | 64 |
1 files changed, 19 insertions, 45 deletions
diff --git a/crypto/bn/bn_nist.c b/crypto/bn/bn_nist.c index 5b6d4e7e4d..4ff320d0bb 100644 --- a/crypto/bn/bn_nist.c +++ b/crypto/bn/bn_nist.c @@ -338,7 +338,6 @@ int BN_nist_mod_192(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, sizeof(unsigned int)]; } buf; BN_ULONG c_d[BN_NIST_192_TOP], *res; - PTR_SIZE_INT mask; static const BIGNUM ossl_bignum_nist_p_192_sqr = { (BN_ULONG *)_nist_p_192_sqr, OSSL_NELEM(_nist_p_192_sqr), @@ -439,13 +438,9 @@ int BN_nist_mod_192(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, * 'tmp=result-modulus; if (!carry || !borrow) result=tmp;' * this is what happens below, but without explicit if:-) a. */ - mask = - 0 - (PTR_SIZE_INT) bn_sub_words(c_d, r_d, _nist_p_192[0], - BN_NIST_192_TOP); - mask &= 0 - (PTR_SIZE_INT) carry; - res = c_d; - res = (BN_ULONG *) - (((PTR_SIZE_INT) res & ~mask) | ((PTR_SIZE_INT) r_d & mask)); + res = (bn_sub_words(c_d, r_d, _nist_p_192[0], BN_NIST_192_TOP) && carry) + ? r_d + : c_d; nist_cp_bn(r_d, res, BN_NIST_192_TOP); r->top = BN_NIST_192_TOP; bn_correct_top(r); @@ -479,7 +474,6 @@ int BN_nist_mod_224(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, sizeof(unsigned int)]; } buf; BN_ULONG c_d[BN_NIST_224_TOP], *res; - PTR_SIZE_INT mask; union { bn_addsub_f f; PTR_SIZE_INT p; @@ -616,19 +610,14 @@ int BN_nist_mod_224(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, carry = (int)bn_add_words(r_d, r_d, _nist_p_224[-carry - 1], BN_NIST_224_TOP); - mask = 0 - (PTR_SIZE_INT) carry; - u.p = ((PTR_SIZE_INT) bn_sub_words & mask) | - ((PTR_SIZE_INT) bn_add_words & ~mask); + u.f = carry ? bn_sub_words : bn_add_words; } else carry = 1; /* otherwise it's effectively same as in BN_nist_mod_192... */ - mask = - 0 - (PTR_SIZE_INT) (*u.f) (c_d, r_d, _nist_p_224[0], BN_NIST_224_TOP); - mask &= 0 - (PTR_SIZE_INT) carry; - res = c_d; - res = (BN_ULONG *)(((PTR_SIZE_INT) res & ~mask) | - ((PTR_SIZE_INT) r_d & mask)); + res = ((*u.f) (c_d, r_d, _nist_p_224[0], BN_NIST_224_TOP) && carry) + ? r_d + : c_d; nist_cp_bn(r_d, res, BN_NIST_224_TOP); r->top = BN_NIST_224_TOP; bn_correct_top(r); @@ -660,7 +649,6 @@ int BN_nist_mod_256(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, sizeof(unsigned int)]; } buf; BN_ULONG c_d[BN_NIST_256_TOP], *res; - PTR_SIZE_INT mask; union { bn_addsub_f f; PTR_SIZE_INT p; @@ -859,18 +847,13 @@ int BN_nist_mod_256(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, carry = (int)bn_add_words(r_d, r_d, _nist_p_256[-carry - 1], BN_NIST_256_TOP); - mask = 0 - (PTR_SIZE_INT) carry; - u.p = ((PTR_SIZE_INT) bn_sub_words & mask) | - ((PTR_SIZE_INT) bn_add_words & ~mask); + u.f = carry ? bn_sub_words : bn_add_words; } else carry = 1; - mask = - 0 - (PTR_SIZE_INT) (*u.f) (c_d, r_d, _nist_p_256[0], BN_NIST_256_TOP); - mask &= 0 - (PTR_SIZE_INT) carry; - res = c_d; - res = (BN_ULONG *)(((PTR_SIZE_INT) res & ~mask) | - ((PTR_SIZE_INT) r_d & mask)); + res = ((*u.f) (c_d, r_d, _nist_p_256[0], BN_NIST_256_TOP) && carry) + ? r_d + : c_d; nist_cp_bn(r_d, res, BN_NIST_256_TOP); r->top = BN_NIST_256_TOP; bn_correct_top(r); @@ -906,7 +889,6 @@ int BN_nist_mod_384(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, sizeof(unsigned int)]; } buf; BN_ULONG c_d[BN_NIST_384_TOP], *res; - PTR_SIZE_INT mask; union { bn_addsub_f f; PTR_SIZE_INT p; @@ -1140,18 +1122,13 @@ int BN_nist_mod_384(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, carry = (int)bn_add_words(r_d, r_d, _nist_p_384[-carry - 1], BN_NIST_384_TOP); - mask = 0 - (PTR_SIZE_INT) carry; - u.p = ((PTR_SIZE_INT) bn_sub_words & mask) | - ((PTR_SIZE_INT) bn_add_words & ~mask); + u.f = carry ? bn_sub_words : bn_add_words; } else carry = 1; - mask = - 0 - (PTR_SIZE_INT) (*u.f) (c_d, r_d, _nist_p_384[0], BN_NIST_384_TOP); - mask &= 0 - (PTR_SIZE_INT) carry; - res = c_d; - res = (BN_ULONG *)(((PTR_SIZE_INT) res & ~mask) | - ((PTR_SIZE_INT) r_d & mask)); + res = ((*u.f) (c_d, r_d, _nist_p_384[0], BN_NIST_384_TOP) && carry) + ? r_d + : c_d; nist_cp_bn(r_d, res, BN_NIST_384_TOP); r->top = BN_NIST_384_TOP; bn_correct_top(r); @@ -1168,7 +1145,6 @@ int BN_nist_mod_521(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, { int top = a->top, i; BN_ULONG *r_d, *a_d = a->d, t_d[BN_NIST_521_TOP], val, tmp, *res; - PTR_SIZE_INT mask; static const BIGNUM ossl_bignum_nist_p_521_sqr = { (BN_ULONG *)_nist_p_521_sqr, OSSL_NELEM(_nist_p_521_sqr), @@ -1221,12 +1197,10 @@ int BN_nist_mod_521(BIGNUM *r, const BIGNUM *a, const BIGNUM *field, r_d[i] &= BN_NIST_521_TOP_MASK; bn_add_words(r_d, r_d, t_d, BN_NIST_521_TOP); - mask = - 0 - (PTR_SIZE_INT) bn_sub_words(t_d, r_d, _nist_p_521, - BN_NIST_521_TOP); - res = t_d; - res = (BN_ULONG *)(((PTR_SIZE_INT) res & ~mask) | - ((PTR_SIZE_INT) r_d & mask)); + res = bn_sub_words(t_d, r_d, _nist_p_521, + BN_NIST_521_TOP) + ? r_d + : t_d; nist_cp_bn(r_d, res, BN_NIST_521_TOP); r->top = BN_NIST_521_TOP; bn_correct_top(r); |