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tls: x25519: code shrink by factoring out common code

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function                                             old     new   delta
fe_reduce                                              -      37     +37
lm_add                                                67      43     -24
fe_mul_c                                              62      38     -24
fe_mul__distinct                                     138     112     -26
curve25519                                           800     767     -33
lm_sub                                                98      64     -34
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/5 up/down: 37/-141)          Total: -104 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2021-12-01 15:09:44 +01:00
parent 8514b4166d
commit b240733ae7
1 changed files with 24 additions and 50 deletions
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74
networking/tls_fe.c
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@ -187,7 +187,7 @@ static void fprime_mul(byte *r, const byte *a, const byte *b,
#if 0 //UNUSED #if 0 //UNUSED
static void fe_load(byte *x, word32 c) static void fe_load(byte *x, word32 c)
{ {
word32 i; int i;
for (i = 0; i < sizeof(c); i++) { for (i = 0; i < sizeof(c); i++) {
x[i] = c; x[i] = c;
@ -199,6 +199,21 @@ static void fe_load(byte *x, word32 c)
} }
#endif #endif
static void fe_reduce(byte *x, word32 c)
{
int i;
/* Reduce using 2^255 = 19 mod p */
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) static void fe_normalize(byte *x)
{ {
byte minusp[F25519_SIZE]; byte minusp[F25519_SIZE];
@ -206,14 +221,7 @@ static void fe_normalize(byte *x)
int i; int i;
/* Reduce using 2^255 = 19 mod p */ /* Reduce using 2^255 = 19 mod p */
c = (x[31] >> 7) * 19; fe_reduce(x, x[31]);
x[31] &= 127;
for (i = 0; i < F25519_SIZE; i++) {
c += x[i];
x[i] = (byte)c;
c >>= 8;
}
/* The number is now less than 2^255 + 18, and therefore less than /* The number is now less than 2^255 + 18, and therefore less than
* 2p. Try subtracting p, and conditionally load the subtracted * 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 */ /* Reduce with 2^255 = 19 mod p */
r[31] &= 127; fe_reduce(r, c);
c = (c >> 7) * 19;
for (i = 0; i < F25519_SIZE; i++) {
c += r[i];
r[i] = (byte)c;
c >>= 8;
}
} }
static void lm_sub(byte* r, const byte* a, const byte* b) 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 */ /* Calculate a + 2p - b, to avoid underflow */
c = 218; 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]); c += 65280 + ((word32)a[i]) - ((word32)b[i]);
r[i] = c; r[i] = c;
c >>= 8; c >>= 8;
} }
c += ((word32)a[31]) - ((word32)b[31]); c += ((word32)a[31]) - ((word32)b[31]);
r[31] = c & 127;
c = (c >> 7) * 19;
for (i = 0; i < F25519_SIZE; i++) { fe_reduce(r, c);
c += r[i];
r[i] = c;
c >>= 8;
}
} }
#if 0 //UNUSED #if 0 //UNUSED
@ -289,21 +284,15 @@ static void lm_neg(byte* r, const byte* a)
/* Calculate 2p - a, to avoid underflow */ /* Calculate 2p - a, to avoid underflow */
c = 218; c = 218;
for (i = 0; i + 1 < F25519_SIZE; i++) { for (i = 0; i < F25519_SIZE - 1; i++) {
c += 65280 - ((word32)a[i]); c += 65280 - ((word32)a[i]);
r[i] = c; r[i] = c;
c >>= 8; c >>= 8;
} }
c -= ((word32)a[31]); c -= ((word32)a[31]);
r[31] = c & 127;
c = (c >> 7) * 19;
for (i = 0; i < F25519_SIZE; i++) { fe_reduce(r, c);
c += r[i];
r[i] = c;
c >>= 8;
}
} }
#endif #endif
@ -326,14 +315,7 @@ static void fe_mul__distinct(byte *r, const byte *a, const byte *b)
r[i] = c; r[i] = c;
} }
r[31] &= 127; fe_reduce(r, c);
c = (c >> 7) * 19;
for (i = 0; i < F25519_SIZE; i++) {
c += r[i];
r[i] = c;
c >>= 8;
}
} }
#if 0 //UNUSED #if 0 //UNUSED
@ -357,15 +339,7 @@ static void fe_mul_c(byte *r, const byte *a, word32 b)
r[i] = c; r[i] = c;
} }
r[31] &= 127; fe_reduce(r, c);
c >>= 7;
c *= 19;
for (i = 0; i < F25519_SIZE; i++) {
c += r[i];
r[i] = c;
c >>= 8;
}
} }
static void fe_inv__distinct(byte *r, const byte *x) static void fe_inv__distinct(byte *r, const byte *x)