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draw_bmp: silence another ridiculous ubsan warning 

UB sanitizer complains that aval<<24 (if >=128) cannot be represented as
int. Indeed, we would shift a bit into the sign of an int, which is
probably UB or implementation defined (I can't even remember, but the
stupidity of it burns). So technically, ubsan might be right.

Change aval to uint32_t, which I don't think has a chance of getting
promoted to int. Change the other *val to uint32_t too for cosmetic
symmetry.

So we have to obscure the intention of the code (*val can take only 8
bits) out of language stupidity. How nice. (What a shitty language.)
This commit is contained in:
wm4 2020-04-18 00:16:52 +02:00
parent ab201ce042
commit a09c7691d7
1 changed files with 4 additions and 4 deletions
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8
sub/draw_bmp.c
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@ -148,10 +148,10 @@ static void unpremultiply_and_split_BGR32(struct mp_image *img,
uint8_t *arow = &alpha->planes[0][alpha->stride[0] * y]; uint8_t *arow = &alpha->planes[0][alpha->stride[0] * y];
for (int x = 0; x < img->w; ++x) { for (int x = 0; x < img->w; ++x) {
uint32_t pval = irow[x]; uint32_t pval = irow[x];
uint8_t aval = (pval >> 24); uint32_t aval = (pval >> 24);
uint8_t rval = (pval >> 16) & 0xFF; uint32_t rval = (pval >> 16) & 0xFF;
uint8_t gval = (pval >> 8) & 0xFF; uint32_t gval = (pval >> 8) & 0xFF;
uint8_t bval = pval & 0xFF; uint32_t bval = pval & 0xFF;
// multiplied = separate * alpha / 255 // multiplied = separate * alpha / 255
// separate = rint(multiplied * 255 / alpha) // separate = rint(multiplied * 255 / alpha)
// = floor(multiplied * 255 / alpha + 0.5) // = floor(multiplied * 255 / alpha + 0.5)