b240733ae
Denys Vlasenko
2021-12-01
Subject
tls: x25519: code shrink by factoring out common code
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networking/tls_fe.c+21 -47
| @@ -187,7 +187,7 @@ static void fprime_mul(byte *r, const byte *a, const byte *b, | |
| #if 0 //UNUSED | |
| static void fe_load(byte *x, word32 c) | |
| { | |
| - | word32 i; |
| + | int i; |
| for (i = 0; i < sizeof(c); i++) { | |
| x[i] = c; | |
| @@ -199,21 +199,29 @@ static void fe_load(byte *x, word32 c) | |
| } | |
| #endif | |
| - | static void fe_normalize(byte *x) |
| + | static void fe_reduce(byte *x, word32 c) |
| { | |
| - | byte minusp[F25519_SIZE]; |
| - | unsigned c; |
| int i; | |
| /* Reduce using 2^255 = 19 mod p */ | |
| - | c = (x[31] >> 7) * 19; |
| - | x[31] &= 127; |
| + | x[31] = c & 127; |
| + | c = (c >> 7) * 19; |
| for (i = 0; i < F25519_SIZE; i++) { | |
| c += x[i]; | |
| x[i] = (byte)c; | |
| c >>= 8; | |
| } | |
| + | } |
| + | |
| + | static void fe_normalize(byte *x) |
| + | { |
| + | byte minusp[F25519_SIZE]; |
| + | unsigned c; |
| + | int i; |
| + | |
| + | /* Reduce using 2^255 = 19 mod p */ |
| + | fe_reduce(x, x[31]); |
| /* The number is now less than 2^255 + 18, and therefore less than | |
| * 2p. Try subtracting p, and conditionally load the subtracted | |
| @@ -247,14 +255,7 @@ static void lm_add(byte* r, const byte* a, const byte* b) | |
| } | |
| /* Reduce with 2^255 = 19 mod p */ | |
| - | r[31] &= 127; |
| - | c = (c >> 7) * 19; |
| - | |
| - | for (i = 0; i < F25519_SIZE; i++) { |
| - | c += r[i]; |
| - | r[i] = (byte)c; |
| - | c >>= 8; |
| - | } |
| + | fe_reduce(r, c); |
| } | |
| static void lm_sub(byte* r, const byte* a, const byte* b) | |
| @@ -264,21 +265,15 @@ static void lm_sub(byte* r, const byte* a, const byte* b) | |
| /* Calculate a + 2p - b, to avoid underflow */ | |
| c = 218; | |
| - | for (i = 0; i + 1 < F25519_SIZE; i++) { |
| + | for (i = 0; i < F25519_SIZE - 1; i++) { |
| c += 65280 + ((word32)a[i]) - ((word32)b[i]); | |
| r[i] = c; | |
| c >>= 8; | |
| } | |
| c += ((word32)a[31]) - ((word32)b[31]); | |
| - | r[31] = c & 127; |
| - | c = (c >> 7) * 19; |
| - | for (i = 0; i < F25519_SIZE; i++) { |
| - | c += r[i]; |
| - | r[i] = c; |
| - | c >>= 8; |
| - | } |
| + | fe_reduce(r, c); |
| } | |
| #if 0 //UNUSED | |
| @@ -289,21 +284,15 @@ static void lm_neg(byte* r, const byte* a) | |
| /* Calculate 2p - a, to avoid underflow */ | |
| c = 218; | |
| - | for (i = 0; i + 1 < F25519_SIZE; i++) { |
| + | for (i = 0; i < F25519_SIZE - 1; i++) { |
| c += 65280 - ((word32)a[i]); | |
| r[i] = c; | |
| c >>= 8; | |
| } | |
| c -= ((word32)a[31]); | |
| - | r[31] = c & 127; |
| - | c = (c >> 7) * 19; |
| - | for (i = 0; i < F25519_SIZE; i++) { |
| - | c += r[i]; |
| - | r[i] = c; |
| - | c >>= 8; |
| - | } |
| + | fe_reduce(r, c); |
| } | |
| #endif | |
| @@ -326,14 +315,7 @@ static void fe_mul__distinct(byte *r, const byte *a, const byte *b) | |
| r[i] = c; | |
| } | |
| - | r[31] &= 127; |
| - | c = (c >> 7) * 19; |
| - | |
| - | for (i = 0; i < F25519_SIZE; i++) { |
| - | c += r[i]; |
| - | r[i] = c; |
| - | c >>= 8; |
| - | } |
| + | fe_reduce(r, c); |
| } | |
| #if 0 //UNUSED | |
| @@ -357,15 +339,7 @@ static void fe_mul_c(byte *r, const byte *a, word32 b) | |
| r[i] = c; | |
| } | |
| - | r[31] &= 127; |
| - | c >>= 7; |
| - | c *= 19; |
| - | |
| - | for (i = 0; i < F25519_SIZE; i++) { |
| - | c += r[i]; |
| - | r[i] = c; |
| - | c >>= 8; |
| - | } |
| + | fe_reduce(r, c); |
| } | |
| static void fe_inv__distinct(byte *r, const byte *x) | |