-rw-r--r-- 2182 lib25519-20220726/crypto_sign/ed25519/amd64-maa4/sc25519_from32bytes.c raw
#include "sc25519.h" /*Arithmetic modulo the group order n = 2^252 + 27742317777372353535851937790883648493 * = 7237005577332262213973186563042994240857116359379907606001950938285454250989 */ /* Contains order, 2*order, 4*order, 8*order, each represented in 4 consecutive unsigned long long */ static const unsigned long long order[16] = {0x5812631A5CF5D3EDULL, 0x14DEF9DEA2F79CD6ULL, 0x0000000000000000ULL, 0x1000000000000000ULL, 0xB024C634B9EBA7DAULL, 0x29BDF3BD45EF39ACULL, 0x0000000000000000ULL, 0x2000000000000000ULL, 0x60498C6973D74FB4ULL, 0x537BE77A8BDE7359ULL, 0x0000000000000000ULL, 0x4000000000000000ULL, 0xC09318D2E7AE9F68ULL, 0xA6F7CEF517BCE6B2ULL, 0x0000000000000000ULL, 0x8000000000000000ULL}; static unsigned long long smaller(unsigned long long a,unsigned long long b) { unsigned long long atop = a >> 32; unsigned long long abot = a & 4294967295; unsigned long long btop = b >> 32; unsigned long long bbot = b & 4294967295; unsigned long long atopbelowbtop = (atop - btop) >> 63; unsigned long long atopeqbtop = ((atop ^ btop) - 1) >> 63; unsigned long long abotbelowbbot = (abot - bbot) >> 63; return atopbelowbtop | (atopeqbtop & abotbelowbbot); } void sc25519_from32bytes(sc25519 *r, const unsigned char x[32]) { unsigned long long t[4]; unsigned long long b; unsigned long long mask; int i, j; /* assuming little-endian */ r->v[0] = *(unsigned long long *)x; r->v[1] = *(((unsigned long long *)x)+1); r->v[2] = *(((unsigned long long *)x)+2); r->v[3] = *(((unsigned long long *)x)+3); for(j=3;j>=0;j--) { b=0; for(i=0;i<4;i++) { b += order[4*j+i]; /* no overflow for this particular order */ t[i] = r->v[i] - b; b = smaller(r->v[i],b); } mask = b - 1; for(i=0;i<4;i++) r->v[i] ^= mask & (r->v[i] ^ t[i]); } }