From 221a06bb16c9b2584de8c9b9a5ca9991ad4a7957 Mon Sep 17 00:00:00 2001
From: Vikas Arora <vikasa@google.com>
Date: Mon, 9 Jan 2012 14:05:28 +0530
Subject: [PATCH] Fix bug for Alpha in RGBA_4444 color-mode.

Fix bug for Alpha data in RGBA_4444 color-mode.
The Alpha data is required to be clipped [0, 15] while
converting from 8 bits to 4 bits.

Change-Id: I80705d575c35121beb9633a05ec8823435c79586
---
 src/dec/io.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/dec/io.c b/src/dec/io.c
index a6a20e94..ed8eb7f6 100644
--- a/src/dec/io.c
+++ b/src/dec/io.c
@@ -202,6 +202,10 @@ static int EmitAlphaRGB(const VP8Io* const io, WebPDecParams* const p) {
   return 0;
 }
 
+static WEBP_INLINE uint32_t clip(uint32_t v, uint32_t max_value) {
+  return (v > max_value) ? max_value : v;
+}
+
 static int EmitAlphaRGBA4444(const VP8Io* const io, WebPDecParams* const p) {
   const int mb_w = io->mb_w;
   const int mb_h = io->mb_h;
@@ -213,7 +217,7 @@ static int EmitAlphaRGBA4444(const VP8Io* const io, WebPDecParams* const p) {
     for (j = 0; j < mb_h; ++j) {
       for (i = 0; i < mb_w; ++i) {
         // Fill in the alpha value (converted to 4 bits).
-        const uint8_t alpha_val = (alpha[i] + 8) >> 4;
+        const uint32_t alpha_val = clip((alpha[i] + 8) >> 4, 15);
         dst[2 * i] = (dst[2 * i] & 0xf0) | alpha_val;
       }
       alpha += io->width;
@@ -490,7 +494,7 @@ static int ExportAlphaRGBA4444(WebPDecParams* const p, int y_pos) {
     ExportRow(&p->scaler_a);
     for (i = 0; i < p->scaler_a.dst_width; ++i) {
       // Fill in the alpha value (converted to 4 bits).
-      const uint8_t alpha_val = (p->scaler_a.dst[i] + 8) >> 4;
+      const uint32_t alpha_val = clip((p->scaler_a.dst[i] + 8) >> 4, 15);
       dst[2 * i] = (dst[2 * i] & 0xf0) | alpha_val;
     }
     dst += buf->stride;