BGD_DECLARE(gdImagePtr) gdImageCreateFromWebpCtx (gdIOCtx * infile)
{
	int    width, height;
	uint8_t   *filedata = NULL;
	uint8_t    *argb = NULL;
	unsigned char   *read, *temp;
	size_t size = 0, n;
	gdImagePtr im;
	int x, y;
	uint8_t *p;

	do {
		temp = gdRealloc(filedata, size+GD_WEBP_ALLOC_STEP);
		if (temp) {
			filedata = temp;
			read = temp + size;
		} else {
			if (filedata) {
				gdFree(filedata);
			}
			gd_error("WebP decode: realloc failed");
			return NULL;
		}

		n = gdGetBuf(read, GD_WEBP_ALLOC_STEP, infile);
		if (n>0 && n!=EOF) {
			size += n;
		}
	} while (n>0 && n!=EOF);

	if (WebPGetInfo(filedata,size, &width, &height) == 0) {
		gd_error("gd-webp cannot get webp info");
		gdFree(temp);
		return NULL;
	}

	im = gdImageCreateTrueColor(width, height);
	if (!im) {
		gdFree(temp);
		return NULL;
	}
	argb = WebPDecodeARGB(filedata, size, &width, &height);
	if (!argb) {
		gd_error("gd-webp cannot allocate temporary buffer");
		gdFree(temp);
		gdImageDestroy(im);
		return NULL;
	}
	for (y = 0, p = argb;  y < height; y++) {
		for (x = 0; x < width; x++) {
			register uint8_t a = gdAlphaMax - (*(p++) >> 1);
			register uint8_t r = *(p++);
			register uint8_t g = *(p++);
			register uint8_t b = *(p++);
			im->tpixels[y][x] = gdTrueColorAlpha(r, g, b, a);
		}
	}
	/* do not use gdFree here, in case gdFree/alloc is mapped to something else than libc */
	free(argb);
	gdFree(temp);
	im->saveAlphaFlag = 1;
	return im;
}

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.