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[scaled-font] Post-process hash value.

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Mix the bits within the hash value to reduce clustering.
This commit is contained in:
Chris Wilson 2008-12-19 13:04:31 +00:00
parent 555dd6b97e
commit 9c9ed8f0b5
1 changed files with 15 additions and 0 deletions
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15
src/cairo-scaled-font.c
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@ -530,6 +530,17 @@ _hash_matrix_fnv (const cairo_matrix_t *matrix,
return hval;
}
static uint32_t
_hash_mix_bits (uint32_t hash)
{
hash += hash << 12;
hash ^= hash >> 7;
hash += hash << 3;
hash ^= hash >> 17;
hash += hash << 5;
return hash;
}
static void
_cairo_scaled_font_init_key (cairo_scaled_font_t *scaled_font,
cairo_font_face_t *font_face,
@ -552,10 +563,14 @@ _cairo_scaled_font_init_key (cairo_scaled_font_t *scaled_font,
/* We do a bytewise hash on the font matrices */
hash = _hash_matrix_fnv (&scaled_font->font_matrix, hash);
hash = _hash_matrix_fnv (&scaled_font->ctm, hash);
hash = _hash_mix_bits (hash);
hash ^= (unsigned long) scaled_font->font_face;
hash ^= cairo_font_options_hash (&scaled_font->options);
/* final mixing of bits */
hash = _hash_mix_bits (hash);
assert (hash != ZOMBIE);
scaled_font->hash_entry.hash = hash;
}