void gdImageWebpCtx (gdImagePtr im, gdIOCtx * outfile, int quantization)
{
	uint8_t *argb;
	int x, y;
	uint8_t *p;
	uint8_t *out;
	size_t out_size;

	if (im == NULL) {
		return;
	}

	if (!gdImageTrueColor(im)) {
		zend_error(E_ERROR, "Paletter image not supported by webp");
		return;
	}

	if (quantization == -1) {
 		quantization = 80;
 	}
 
	if (overflow2(gdImageSX(im), 4)) {
		return;
	}

	if (overflow2(gdImageSX(im) * 4, gdImageSY(im))) {
		return;
	}

 	argb = (uint8_t *)gdMalloc(gdImageSX(im) * 4 * gdImageSY(im));
 	if (!argb) {
 		return;
	}
	p = argb;
	for (y = 0; y < gdImageSY(im); y++) {
		for (x = 0; x < gdImageSX(im); x++) {
			register int c;
			register char a;
			c = im->tpixels[y][x];
			a = gdTrueColorGetAlpha(c);
			if (a == 127) {
				a = 0;
			} else {
				a = 255 - ((a << 1) + (a >> 6));
			}
			*(p++) = gdTrueColorGetRed(c);
			*(p++) = gdTrueColorGetGreen(c);
			*(p++) = gdTrueColorGetBlue(c); 
			*(p++) = a;
		}
	}
	out_size = WebPEncodeRGBA(argb, gdImageSX(im), gdImageSY(im), gdImageSX(im) * 4, quantization, &out);
	if (out_size == 0) {
		zend_error(E_ERROR, "gd-webp encoding failed");
		goto freeargb;
	}
	gdPutBuf(out, out_size, outfile);
	free(out);

freeargb:
	gdFree(argb);
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.