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crypto: STD-compliant shifting in sc_check()

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jeffro256
2026-03-21 22:34:01 -10:00
parent b9998fc9e1
commit c5be4dda1c
1 changed files with 19 additions and 1 deletions
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src/crypto/crypto-ops.c
+19 -1
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@@ -3810,6 +3810,15 @@ static int64_t signum(int64_t a) {
return a > 0 ? 1 : a < 0 ? -1 : 0;
}
//! @brief arithmetic left shift for signed operands
static int64_t signed_lshift(const int64_t a, const int b) {
#ifdef __GNUC__
return a << b; // well-defined in GCC
#else
return a * ((int64_t)1 << b);
#endif
}
int sc_check(const unsigned char *s) {
int64_t s0 = load_4(s);
int64_t s1 = load_4(s + 4);
@@ -3819,7 +3828,16 @@ int sc_check(const unsigned char *s) {
int64_t s5 = load_4(s + 20);
int64_t s6 = load_4(s + 24);
int64_t s7 = load_4(s + 28);
return (signum(1559614444 - s0) + (signum(1477600026 - s1) << 1) + (signum(2734136534 - s2) << 2) + (signum(350157278 - s3) << 3) + (signum(-s4) << 4) + (signum(-s5) << 5) + (signum(-s6) << 6) + (signum(268435456 - s7) << 7)) >> 8;
return -(0 >
( signum(1559614444 - s0)
+ signed_lshift(signum(1477600026 - s1), 1)
+ signed_lshift(signum(2734136534 - s2), 2)
+ signed_lshift(signum(350157278 - s3), 3)
+ signed_lshift(signum( - s4), 4)
+ signed_lshift(signum( - s5), 5)
+ signed_lshift(signum( - s6), 6)
+ signed_lshift(signum(268435456 - s7), 7)
));
}
int sc_isnonzero(const unsigned char *s) {