Function GetLineLength

include/bmpread/bmpread.c:515–529

Returns the byte length of a scan line padded as necessary to be divisible * by four. For example, 3 pixels wide at 24 bpp would yield 12 (3 pixels * 3 * bytes each = 9 bytes, padded by 3 to the next multiple of 4). bpp is *bits* * per pixel, not bytes. Returns 0 in case of overflow. */

 * per pixel, not bytes.  Returns 0 in case of overflow.
 */
static size_t GetLineLength(size_t width, size_t bpp)
{
    size_t bits = width * bpp;
    size_t pad_bits = (32 - (bits & 0x1f)) & 0x1f; /* x & 0x1f == x % 32 */

    /* Check for overflow, in both the above multiplication and the below
     * addition.  It's well defined to do this in any order relative to the
     * operations themselves (since size_t is unsigned), so we combine the
     * checks into one if.  bpp has been checked for being nonzero elsewhere.
     */
    if(!CanMultiply(width, bpp) || !CanAdd(bits, pad_bits)) return 0;

    /* Convert to bytes. */
    return (bits + pad_bits) / 8;
}

/* Reads and validates the bitmap header metadata from the context's file
 * object.  Assumes the file pointer is at the start of the file.  Returns 1 if