[FFmpeg-devel] [PATCH] lavc/ccaption_dec: simplify parity check

[Clément Bœsch]

---
 libavcodec/ccaption_dec.c | 43 +++++++------------------------------------
 1 file changed, 7 insertions(+), 36 deletions(-)

diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
index 9f67caa..1fdf7ed 100644
--- a/libavcodec/ccaption_dec.c
+++ b/libavcodec/ccaption_dec.c
@@ -101,40 +101,6 @@ static const unsigned char pac2_attribs[32][3] = // Color, font, ident
     /* total 32 entries */
 };
 
-/* 0-255 needs 256 spaces */
-static const uint8_t parity_table[256] = { 0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           0, 1, 1, 0, 1, 0, 0, 1,
-                                           1, 0, 0, 1, 0, 1, 1, 0 };
-
 struct Screen {
     /* +1 is used to compensate null character of string */
     uint8_t characters[SCREEN_ROWS][SCREEN_COLUMNS+1];
@@ -221,6 +187,11 @@ static int write_char (CCaptionSubContext *ctx, char *row,uint8_t col, char ch)
     }
 }
 
+static inline int get_parity(uint8_t x)
+{
+    return (0x6996966996696996ULL >> (x & 63) ^ (x>>7) ^ (x>>6)) & 1;
+}
+
 /**
  * This function after validating parity bit, also remove it from data pair.
  * The first byte doesn't pass parity, we replace it with a solid blank
@@ -238,10 +209,10 @@ static int validate_cc_data_pair (uint8_t *cc_data_pair)
 
     // if EIA-608 data then verify parity.
     if (cc_type==0 || cc_type==1) {
-        if (!parity_table[cc_data_pair[2]]) {
+        if (!get_parity(cc_data_pair[2])) {
             return AVERROR_INVALIDDATA;
         }
-        if (!parity_table[cc_data_pair[1]]) {
+        if (!get_parity(cc_data_pair[1])) {
             cc_data_pair[1]=0x7F;
         }
     }
-- 
2.6.4