X-Git-Url: https://wimlib.net/git/?a=blobdiff_plain;f=src%2Flzx-common.c;h=d733ada7d8d073b76a86fc2a041de0154d835e81;hb=acabf4f97fdf439d6f95ff7af1fa952e91fa483b;hp=b2eeb7d1e54f1bbdfcabbae8d708ff8fd7e220d4;hpb=522227d4c6cc53ee966162b095ec908bdeb5a023;p=wimlib diff --git a/src/lzx-common.c b/src/lzx-common.c index b2eeb7d1..d733ada7 100644 --- a/src/lzx-common.c +++ b/src/lzx-common.c @@ -33,9 +33,9 @@ # include #endif -/* Mapping: position slot => first match offset that uses that position slot. +/* Mapping: offset slot => first match offset that uses that offset slot. */ -const u32 lzx_position_base[LZX_MAX_POSITION_SLOTS] = { +const u32 lzx_offset_slot_base[LZX_MAX_OFFSET_SLOTS] = { 0 , 1 , 2 , 3 , 4 , /* 0 --- 4 */ 6 , 8 , 12 , 16 , 24 , /* 5 --- 9 */ 32 , 48 , 64 , 96 , 128 , /* 10 --- 14 */ @@ -49,10 +49,9 @@ const u32 lzx_position_base[LZX_MAX_POSITION_SLOTS] = { 2097152 /* 50 */ }; -/* Mapping: position slot => how many extra bits must be read and added to the - * corresponding position base to decode the match offset. */ -#ifdef USE_LZX_EXTRA_BITS_ARRAY -const u8 lzx_extra_bits[LZX_MAX_POSITION_SLOTS] = { +/* Mapping: offset slot => how many extra bits must be read and added to the + * corresponding offset slot base to decode the match offset. */ +const u8 lzx_extra_offset_bits[LZX_MAX_OFFSET_SLOTS] = { 0 , 0 , 0 , 0 , 1 , 1 , 2 , 2 , 3 , 3 , 4 , 4 , 5 , 5 , 6 , @@ -65,53 +64,61 @@ const u8 lzx_extra_bits[LZX_MAX_POSITION_SLOTS] = { 17, 17, 17, 17, 17, 17 }; -#endif -/* LZX window size must be a power of 2 between 2^15 and 2^21, inclusively. */ -bool -lzx_window_size_valid(size_t window_size) +/* Round the specified compression block size (not LZX block size) up to the + * next valid LZX window size, and return its order (log2). Or, if the block + * size is 0 or greater than the largest valid LZX window size, return 0. */ +unsigned +lzx_get_window_order(size_t max_block_size) { - if (window_size == 0 || (u32)window_size != window_size) - return false; - u32 order = bsr32(window_size); - if (window_size != 1U << order) - return false; - return (order >= LZX_MIN_WINDOW_ORDER && order <= LZX_MAX_WINDOW_ORDER); + unsigned order; + + if (max_block_size == 0 || max_block_size > LZX_MAX_WINDOW_SIZE) + return 0; + + order = bsr32(max_block_size); + + if (((u32)1 << order) != max_block_size) + order++; + + return max(order, LZX_MIN_WINDOW_ORDER); } -/* Given a valid LZX window size, return the number of symbols that will exist +/* Given a valid LZX window order, return the number of symbols that will exist * in the main Huffman code. */ unsigned -lzx_get_num_main_syms(u32 window_size) +lzx_get_num_main_syms(unsigned window_order) { + u32 window_size = (u32)1 << window_order; + /* NOTE: the calculation *should* be as follows: * * u32 max_offset = window_size - LZX_MIN_MATCH_LEN; - * u32 max_formatted_offset = max_offset + LZX_OFFSET_OFFSET; - * u32 num_position_slots = 1 + lzx_get_position_slot_raw(max_formatted_offset); + * u32 max_adjusted_offset = max_offset + LZX_OFFSET_OFFSET; + * u32 num_offset_slots = 1 + lzx_get_offset_slot_raw(max_adjusted_offset); * * However since LZX_MIN_MATCH_LEN == LZX_OFFSET_OFFSET, we would get - * max_formatted_offset == window_size, which would bump the number of - * position slots up by 1 since every valid LZX window size is equal to - * a position base value. The format doesn't do this, and instead + * max_adjusted_offset == window_size, which would bump the number of + * offset slots up by 1 since every valid LZX window size is equal to a + * offset slot base value. The format doesn't do this, and instead * disallows matches with minimum length and maximum offset. This sets - * max_formatted_offset = window_size - 1, so instead we must calculate: + * max_adjusted_offset = window_size - 1, so instead we must calculate: * - * num_position_slots = 1 + lzx_get_position_slot_raw(window_size - 1); + * num_offset_slots = 1 + lzx_get_offset_slot_raw(window_size - 1); * * ... which is the same as * - * num_position_slots = lzx_get_position_slot_raw(window_size); + * num_offset_slots = lzx_get_offset_slot_raw(window_size); * - * ... since every valid window size is equal to a position base value. + * ... since every valid window size is equal to an offset base value. */ - unsigned num_position_slots = lzx_get_position_slot_raw(window_size); + unsigned num_offset_slots = lzx_get_offset_slot_raw(window_size); /* Now calculate the number of main symbols as LZX_NUM_CHARS literal - * symbols, plus 8 symbols per position slot (since there are 8 possible - * length headers, and we need all (position slot, length header) + * symbols, plus 8 symbols per offset slot (since there are 8 possible + * length headers, and we need all (offset slot, length header) * combinations). */ - return LZX_NUM_CHARS + (num_position_slots << 3); + return LZX_NUM_CHARS + (num_offset_slots << 3); } static void