Improve readability of alpha-blending sections

1 files changed, 4 insertions, 2 deletions

diff --git a/ff2ppm.c b/ff2ppm.c
index 4383dc4..b34d870 100644
--- a/ff2ppm.c
+++ b/ff2ppm.c
@@ -66,9 +66,11 @@ main(int argc, char *argv[])
 		for (j = 0, k = 0; j < rowlen; j += 4, k += 3) {
 			a = ntohs(row[j + 3]);
 			for (l = 0; l < 3; l++) {
+				/* alpha blending and 8-bit-reduction */
 				rowout[k + l] = (a * ntohs(row[j + l]) +
-				                 (65535 - a) * mask[l]) /
-				                (257 * 65535);
+				                 (UINT16_MAX - a) * mask[l]) /
+				                (UINT16_MAX *
+						 (UINT16_MAX / UINT8_MAX));
 			}
 		}
 		if (fwrite(rowout, sizeof(uint8_t), rowoutlen, stdout) != rowoutlen) {