avcodec/xpmdec: Use LUT for hex char->number conversion

Speeds up decoding and also reduces binary size.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/xpmdec.c

@@ -193,15 +193,22 @@ static const ColorEntry color_table[] = {
 
 static unsigned hex_char_to_number(uint8_t x)
 {
-    if (x >= 'a' && x <= 'f')
-        x -= 'a' - 10;
-    else if (x >= 'A' && x <= 'F')
-        x -= 'A' - 10;
-    else if (x >= '0' && x <= '9')
-        x -= '0';
-    else
-        x = 0;
-    return x;
+#define TIMES256(idx) \
+TIMES64(4 * (idx)) TIMES64(4 * (idx) + 1) TIMES64(4 * (idx) + 2) TIMES64(4 * (idx) + 3)
+#define TIMES64(idx) \
+TIMES16(4 * (idx)) TIMES16(4 * (idx) + 1) TIMES16(4 * (idx) + 2) TIMES16(4 * (idx) + 3)
+#define TIMES16(idx) \
+TIMES4(4 * (idx)) TIMES4(4 * (idx) + 1) TIMES4(4 * (idx) + 2) TIMES4(4 * (idx) + 3)
+#define TIMES4(idx) \
+ENTRY(4 * (idx)) ENTRY(4 * (idx) + 1) ENTRY(4 * (idx) + 2) ENTRY(4 * (idx) + 3)
+#define ENTRY(x) [x] = ((x) >= 'a' && (x) <= 'f') ? (x) - ('a' - 10) : \
+                       ((x) >= 'A' && (x) <= 'F') ? (x) - ('A' - 10) : \
+                       ((x) >= '0' && (x) <= '9') ? (x) - '0' : 0,
+
+    static const uint8_t lut[] = {
+        TIMES256(0)
+    };
+    return lut[x];
 }
 
 /*