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png: Optimize by avoiding divisions.

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This commit is contained in:
Vladimir Serbinenko 2015-02-26 18:27:43 +01:00
parent 80310ad07d
commit 18125877ee
1 changed files with 20 additions and 9 deletions
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17
grub-core/video/readers/png.c
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@ -227,7 +227,7 @@ grub_png_decode_image_palette (struct grub_png_data *data,
{ {
unsigned i = 0, j; unsigned i = 0, j;
if (len == 0 || len % 3 != 0) if (len == 0)
return GRUB_ERR_NONE; return GRUB_ERR_NONE;
for (i = 0; 3 * i < len && i < 256; i++) for (i = 0; 3 * i < len && i < 256; i++)
@ -851,15 +851,26 @@ grub_png_convert_image (struct grub_png_data *data)
int mask = (1 << data->color_bits) - 1; int mask = (1 << data->color_bits) - 1;
unsigned j; unsigned j;
if (data->is_gray) if (data->is_gray)
{
/* Generic formula is
(0xff * i) / ((1U << data->color_bits) - 1)
but for allowed bit depth of 1, 2 and for it's
equivalent to
(0xff / ((1U << data->color_bits) - 1)) * i
Precompute the multipliers to avoid division.
*/
const grub_uint8_t multipliers[5] = { 0xff, 0xff, 0x55, 0x24, 0x11 };
for (i = 0; i < (1U << data->color_bits); i++) for (i = 0; i < (1U << data->color_bits); i++)
{ {
grub_uint8_t col = (0xff * i) / ((1U << data->color_bits) - 1); grub_uint8_t col = multipliers[data->color_bits] * i;
palette[i][0] = col; palette[i][0] = col;
palette[i][1] = col; palette[i][1] = col;
palette[i][2] = col; palette[i][2] = col;
} }
}
else else
grub_memcpy (palette, data->palette, 16 * 3); grub_memcpy (palette, data->palette, 3 << data->color_bits);
d1c = d1; d1c = d1;
d2c = d2; d2c = d2;
for (j = 0; j < data->image_height; j++, d1c += data->image_width * 3, for (j = 0; j < data->image_height; j++, d1c += data->image_width * 3,