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premultiplied-argb: avoid undefined behavior #134

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premultiplied-argb: avoid undefined behavior #134

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4 changes: 3 additions & 1 deletion docs/premultiplied-argb/index.md
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Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,9 @@ for (int64_t i = 0; i < w * h; i++) {
uint8_t r = 255 * ((pixel >> 16) & 0xff) / a;
uint8_t g = 255 * ((pixel >> 8) & 0xff) / a;
uint8_t b = 255 * (pixel & 0xff) / a;
out[i] = GUINT32_TO_BE(r << 24 | g << 16 | b << 8);
// uint32_t cast avoids undefined behavior: left shift into sign bit
// after r is promoted to int.
out[i] = GUINT32_TO_BE((uint32_t) r << 24 | g << 16 | b << 8);
}
}
```
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