glyph-pixmaps merged
Edgar Toernig
froese at gmx.de
Sat Oct 20 20:11:40 PDT 2007
Keith Packard wrote:
>
> We need a strong hash function as this replaces the previous weak hash +
> memcmp when checking incoming glyphs for matches with the existing set
> of server-resident glyphs. One could argue that this must be
> cryptographically secure to avoid applications uploading misleading
> glyph images.
>
> Patches to use alternate SHA1 implementation would also be welcome, if
> anyone has reason to choose other bits.
Below is a modified sha1 routine. The algorithm has been kept
but support for byte streams and byte-order independence has
been dropped. That simplifies the code and makes it faster.
Compiles to about 700 bytes on x86 and is public domain.
Ciao, ET.
----8<----
#include <sys/types.h>
#include <string.h>
typedef unsigned int u32;
#define f1(x,y,z) (z ^ (x & (y ^ z))) /* x ? y : z */
#define f2(x,y,z) (x ^ y ^ z) /* xor */
#define f3(x,y,z) ((x & y) + (z & (x ^ y))) /* majority */
#define K1 0x5A827999L /* Rounds 0-19: sqrt(2) * 2^30 */
#define K2 0x6ED9EBA1L /* Rounds 20-39: sqrt(3) * 2^30 */
#define K3 0x8F1BBCDCL /* Rounds 40-59: sqrt(5) * 2^30 */
#define K4 0xCA62C1D6L /* Rounds 60-79: sqrt(10) * 2^30 */
static inline u32
rol32(u32 val, int n)
{
return (val << n) | (val >> (32 - n));
}
static void
sha1(u32 digest[5], u32 *W)
{
u32 a, b, c, d, e, t;
int i;
for (i = 0; i < 64; i++)
W[i+16] = rol32(W[i+13] ^ W[i+8] ^ W[i+2] ^ W[i], 1);
a = digest[0];
b = digest[1];
c = digest[2];
d = digest[3];
e = digest[4];
for (i = 0; i < 20; i++)
{
t = f1(b, c, d) + K1 + rol32(a, 5) + e + W[i];
e = d; d = c; c = rol32(b, 30); b = a; a = t;
}
for (; i < 40; i++)
{
t = f2(b, c, d) + K2 + rol32(a, 5) + e + W[i];
e = d; d = c; c = rol32(b, 30); b = a; a = t;
}
for (; i < 60; i++)
{
t = f3(b, c, d) + K3 + rol32(a, 5) + e + W[i];
e = d; d = c; c = rol32(b, 30); b = a; a = t;
}
for (; i < 80; i++)
{
t = f2(b, c, d) + K4 + rol32(a, 5) + e + W[i];
e = d; d = c; c = rol32(b, 30); b = a; a = t;
}
digest[0] += a;
digest[1] += b;
digest[2] += c;
digest[3] += d;
digest[4] += e;
}
void
hash_buffer(u32 digest[5], char *buf, size_t n)
{
u32 W[80];
u32 size = n;
digest[0] = 0x67452301;
digest[1] = 0xefcdab89;
digest[2] = 0x98badcfe;
digest[3] = 0x10325476;
digest[4] = 0xc3d2e1f0;
if (n < 64)
memset((char *)W + n, 0, 64 - n);
while (n >= 64)
{
memcpy((char *)W, buf, 64);
sha1(digest, W);
buf += 64;
n -= 64;
}
if (n > 0)
memcpy((char *)W, buf, n);
if (n > 60)
sha1(digest, W);
W[15] = size;
sha1(digest, W);
}
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