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vga: optimize ppm_save() divisions

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ppm_save() spends upwards of 50% of its time doing divisions. Replace them
with shifts.

Reviewed-by: Alon Levy <alevy@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Avi Kivity 2012-01-03 15:32:57 +02:00 committed by Anthony Liguori
parent 19bf7c8708
commit a0f426109e
1 changed files with 4 additions and 6 deletions
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10
hw/vga.c
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@ -2373,12 +2373,10 @@ int ppm_save(const char *filename, struct DisplaySurface *ds)
v = *(uint32_t *)d;
else
v = (uint32_t) (*(uint16_t *)d);
r = ((v >> ds->pf.rshift) & ds->pf.rmax) * 256 /
(ds->pf.rmax + 1);
g = ((v >> ds->pf.gshift) & ds->pf.gmax) * 256 /
(ds->pf.gmax + 1);
b = ((v >> ds->pf.bshift) & ds->pf.bmax) * 256 /
(ds->pf.bmax + 1);
/* Limited to 8 or fewer bits per channel: */
r = ((v >> ds->pf.rshift) & ds->pf.rmax) << (8 - ds->pf.rbits);
g = ((v >> ds->pf.gshift) & ds->pf.gmax) << (8 - ds->pf.gbits);
b = ((v >> ds->pf.bshift) & ds->pf.bmax) << (8 - ds->pf.bbits);
*pbuf++ = r;
*pbuf++ = g;
*pbuf++ = b;