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Replace the "clever trick" with the popcount intrinsic #19

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Replace the "clever trick" with the popcount intrinsic #19

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23 changes: 4 additions & 19 deletions waif.c
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Original file line number Diff line number Diff line change
Expand Up @@ -42,21 +42,6 @@ static waif_count_type waif_count = 0;
#define MAP_PROP(Mmap, Mbit) (Mmap)[(Mbit) / 32] |= 1 << ((Mbit) % 32)
#define N_MAPPABLE_PROPS (WAIF_MAPSZ * 32)

static int
count_set_bits(uint32_t x)
{
register uint32_t i = x; /* take no chances! */

/* clever trick for adding bits together in parallel to count them */
i = ((i & 0xAAAAAAAA) >> 1) + (i & ~0xAAAAAAAA);
i = ((i & 0xCCCCCCCC) >> 2) + (i & ~0xCCCCCCCC);
i = ((i & 0xF0F0F0F0) >> 4) + (i & ~0xF0F0F0F0);
i = ((i & 0xFF00FF00) >> 8) + (i & ~0xFF00FF00);
i = ((i & 0xFFFF0000) >> 16) + (i & ~0xFFFF0000);

return i;
}

void
free_waif_propdefs(WaifPropdefs *wpd)
{
Expand Down Expand Up @@ -193,7 +178,7 @@ count_waif_propvals(Waif *w)
if (i < 0)
i = 0;
for (j = 0; j < WAIF_MAPSZ; ++j)
i += count_set_bits(w->u.pmap[j]);
i += __builtin_popcountg(w->u.pmap[j]);
return i;
}

Expand Down Expand Up @@ -350,7 +335,7 @@ find_propval_offset(Waif *w, const char *name, int *pidx)
* unmappable propvals which are always allocated.
*/
for (idx = j = 0; j < WAIF_MAPSZ; ++j)
idx += count_set_bits(w->u.pmap[j]);
idx += __builtin_popcountg(w->u.pmap[j]);
return i - N_MAPPABLE_PROPS + idx;
} else if (!PROP_MAPPED(w->u.pmap, i)) {
/* property unmapped, so it's clear */
Expand All @@ -360,11 +345,11 @@ find_propval_offset(Waif *w, const char *name, int *pidx)
* word to the right of the bit we found
*/
for (idx = j = 0; j < i / 32; ++j)
idx += count_set_bits(w->u.pmap[j]);
idx += __builtin_popcountg(w->u.pmap[j]);
if (i % 32 != 0) {
uint32_t mask = -1;
mask >>= 32 - i % 32;
idx += count_set_bits(w->u.pmap[j] & mask);
idx += __builtin_popcountg(w->u.pmap[j] & mask);
}
return idx;
}
Expand Down