diff options
| -rw-r--r-- | src/spu_dec/cc_decoder.c | 82 |
1 files changed, 51 insertions, 31 deletions
diff --git a/src/spu_dec/cc_decoder.c b/src/spu_dec/cc_decoder.c index e8fc09895..2ddd5e102 100644 --- a/src/spu_dec/cc_decoder.c +++ b/src/spu_dec/cc_decoder.c @@ -233,10 +233,58 @@ static const char specialchar[] = { /* character translation table - EIA 608 codes are not all the same as ASCII */ static char chartbl[128]; -/* CC codes use odd parity for error detection, since they originally were */ -/* transmitted via noisy video signals */ -static int parity_table[256]; +/** + * @brief Parity table for packets + * + * CC codes use odd parity for error detection, since they originally were + * transmitted via noisy video signals. + * + * The code to produce the parity table would be the following: + * + * static int parity(uint8_t byte) + * { + * int i; + * int ones = 0; + * + * for (i = 0; i < 7; i++) { + * if (byte & (1 << i)) + * ones++; + * } + * + * return ones & 1; + * } + * + * static void build_parity_table(void) + * { + * uint8_t byte; + * int parity_v; + * for (byte = 0; byte <= 127; byte++) { + * parity_v = parity(byte); + * // CC uses odd parity (i.e., # of 1's in byte is odd.) + * parity_table[byte] = parity_v; + * parity_table[byte | 0x80] = !parity_v; + * } + * } + */ +static const int 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 +}; /*---------------- decoder data structures -----------------------*/ @@ -386,33 +434,6 @@ static void get_font_metrics(osd_renderer_t *renderer, } -static int parity(uint8_t byte) -{ - int i; - int ones = 0; - - for (i = 0; i < 7; i++) { - if (byte & (1 << i)) - ones++; - } - - return ones & 1; -} - - -static void build_parity_table(void) -{ - uint8_t byte; - int parity_v; - for (byte = 0; byte <= 127; byte++) { - parity_v = parity(byte); - /* CC uses odd parity (i.e., # of 1's in byte is odd.) */ - parity_table[byte] = parity_v; - parity_table[byte | 0x80] = !parity_v; - } -} - - static int good_parity(uint16_t data) { int ret = parity_table[data & 0xff] && parity_table[(data & 0xff00) >> 8]; @@ -1478,7 +1499,6 @@ void cc_decoder_close(cc_decoder_t *this) void cc_decoder_init(void) { - build_parity_table(); build_char_table(); } |