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Diffstat (limited to 'utils/rbutilqt/mspack/readbits.h')
-rw-r--r-- | utils/rbutilqt/mspack/readbits.h | 207 |
1 files changed, 207 insertions, 0 deletions
diff --git a/utils/rbutilqt/mspack/readbits.h b/utils/rbutilqt/mspack/readbits.h new file mode 100644 index 0000000000..9b237a3693 --- /dev/null +++ b/utils/rbutilqt/mspack/readbits.h @@ -0,0 +1,207 @@ +/* This file is part of libmspack. + * (C) 2003-2010 Stuart Caie. + * + * libmspack is free software; you can redistribute it and/or modify it under + * the terms of the GNU Lesser General Public License (LGPL) version 2.1 + * + * For further details, see the file COPYING.LIB distributed with libmspack + */ + +#ifndef MSPACK_READBITS_H +#define MSPACK_READBITS_H 1 + +/* this header defines macros that read data streams by + * the individual bits + * + * INIT_BITS initialises bitstream state in state structure + * STORE_BITS stores bitstream state in state structure + * RESTORE_BITS restores bitstream state from state structure + * ENSURE_BITS(n) ensure there are at least N bits in the bit buffer + * READ_BITS(var,n) takes N bits from the buffer and puts them in var + * PEEK_BITS(n) extracts without removing N bits from the bit buffer + * REMOVE_BITS(n) removes N bits from the bit buffer + * + * READ_BITS simply calls ENSURE_BITS, PEEK_BITS and REMOVE_BITS, + * which means it's limited to reading the number of bits you can + * ensure at any one time. It also fails if asked to read zero bits. + * If you need to read zero bits, or more bits than can be ensured in + * one go, use READ_MANY_BITS instead. + * + * These macros have variable names baked into them, so to use them + * you have to define some macros: + * - BITS_TYPE: the type name of your state structure + * - BITS_VAR: the variable that points to your state structure + * - define BITS_ORDER_MSB if bits are read from the MSB, or + * define BITS_ORDER_LSB if bits are read from the LSB + * - READ_BYTES: some code that reads more data into the bit buffer, + * it should use READ_IF_NEEDED (calls read_input if the byte buffer + * is empty), then INJECT_BITS(data,n) to put data from the byte + * buffer into the bit buffer. + * + * You also need to define some variables and structure members: + * - unsigned char *i_ptr; // current position in the byte buffer + * - unsigned char *i_end; // end of the byte buffer + * - unsigned int bit_buffer; // the bit buffer itself + * - unsigned int bits_left; // number of bits remaining + * + * If you use read_input() and READ_IF_NEEDED, they also expect these + * structure members: + * - struct mspack_system *sys; // to access sys->read() + * - unsigned int error; // to record/return read errors + * - unsigned char input_end; // to mark reaching the EOF + * - unsigned char *inbuf; // the input byte buffer + * - unsigned int inbuf_size; // the size of the input byte buffer + * + * Your READ_BYTES implementation should read data from *i_ptr and + * put them in the bit buffer. READ_IF_NEEDED will call read_input() + * if i_ptr reaches i_end, and will fill up inbuf and set i_ptr to + * the start of inbuf and i_end to the end of inbuf. + * + * If you're reading in MSB order, the routines work by using the area + * beyond the MSB and the LSB of the bit buffer as a free source of + * zeroes when shifting. This avoids having to mask any bits. So we + * have to know the bit width of the bit buffer variable. We use + * <limits.h> and CHAR_BIT to find the size of the bit buffer in bits. + * + * If you are reading in LSB order, bits need to be masked. Normally + * this is done by computing the mask: N bits are masked by the value + * (1<<N)-1). However, you can define BITS_LSB_TABLE to use a lookup + * table instead of computing this. This adds two new macros, + * PEEK_BITS_T and READ_BITS_T which work the same way as PEEK_BITS + * and READ_BITS, except they use this lookup table. This is useful if + * you need to look up a number of bits that are only known at + * runtime, so the bit mask can't be turned into a constant by the + * compiler. + + * The bit buffer datatype should be at least 32 bits wide: it must be + * possible to ENSURE_BITS(17), so it must be possible to add 16 new bits + * to the bit buffer when the bit buffer already has 1 to 15 bits left. + */ + +#ifndef BITS_VAR +# error "define BITS_VAR as the state structure poiner variable name" +#endif +#ifndef BITS_TYPE +# error "define BITS_TYPE as the state structure type" +#endif +#if defined(BITS_ORDER_MSB) && defined(BITS_ORDER_LSB) +# error "you must define either BITS_ORDER_MSB or BITS_ORDER_LSB" +#else +# if !(defined(BITS_ORDER_MSB) || defined(BITS_ORDER_LSB)) +# error "you must define BITS_ORDER_MSB or BITS_ORDER_LSB" +# endif +#endif + +#if HAVE_LIMITS_H +# include <limits.h> +#endif +#ifndef CHAR_BIT +# define CHAR_BIT (8) +#endif +#define BITBUF_WIDTH (sizeof(bit_buffer) * CHAR_BIT) + +#define INIT_BITS do { \ + BITS_VAR->i_ptr = &BITS_VAR->inbuf[0]; \ + BITS_VAR->i_end = &BITS_VAR->inbuf[0]; \ + BITS_VAR->bit_buffer = 0; \ + BITS_VAR->bits_left = 0; \ + BITS_VAR->input_end = 0; \ +} while (0) + +#define STORE_BITS do { \ + BITS_VAR->i_ptr = i_ptr; \ + BITS_VAR->i_end = i_end; \ + BITS_VAR->bit_buffer = bit_buffer; \ + BITS_VAR->bits_left = bits_left; \ +} while (0) + +#define RESTORE_BITS do { \ + i_ptr = BITS_VAR->i_ptr; \ + i_end = BITS_VAR->i_end; \ + bit_buffer = BITS_VAR->bit_buffer; \ + bits_left = BITS_VAR->bits_left; \ +} while (0) + +#define ENSURE_BITS(nbits) do { \ + while (bits_left < (nbits)) READ_BYTES; \ +} while (0) + +#define READ_BITS(val, nbits) do { \ + ENSURE_BITS(nbits); \ + (val) = PEEK_BITS(nbits); \ + REMOVE_BITS(nbits); \ +} while (0) + +#define READ_MANY_BITS(val, bits) do { \ + unsigned char needed = (bits), bitrun; \ + (val) = 0; \ + while (needed > 0) { \ + if (bits_left <= (BITBUF_WIDTH - 16)) READ_BYTES; \ + bitrun = (bits_left < needed) ? bits_left : needed; \ + (val) = ((val) << bitrun) | PEEK_BITS(bitrun); \ + REMOVE_BITS(bitrun); \ + needed -= bitrun; \ + } \ +} while (0) + +#ifdef BITS_ORDER_MSB +# define PEEK_BITS(nbits) (bit_buffer >> (BITBUF_WIDTH - (nbits))) +# define REMOVE_BITS(nbits) ((bit_buffer <<= (nbits)), (bits_left -= (nbits))) +# define INJECT_BITS(bitdata,nbits) ((bit_buffer |= \ + (bitdata) << (BITBUF_WIDTH - (nbits) - bits_left)), (bits_left += (nbits))) +#else /* BITS_ORDER_LSB */ +# define PEEK_BITS(nbits) (bit_buffer & ((1 << (nbits))-1)) +# define REMOVE_BITS(nbits) ((bit_buffer >>= (nbits)), (bits_left -= (nbits))) +# define INJECT_BITS(bitdata,nbits) ((bit_buffer |= \ + (bitdata) << bits_left), (bits_left += (nbits))) +#endif + +#ifdef BITS_LSB_TABLE +/* lsb_bit_mask[n] = (1 << n) - 1 */ +static const unsigned short lsb_bit_mask[17] = { + 0x0000, 0x0001, 0x0003, 0x0007, 0x000f, 0x001f, 0x003f, 0x007f, 0x00ff, + 0x01ff, 0x03ff, 0x07ff, 0x0fff, 0x1fff, 0x3fff, 0x7fff, 0xffff +}; +# define PEEK_BITS_T(nbits) (bit_buffer & lsb_bit_mask[(nbits)]) +# define READ_BITS_T(val, nbits) do { \ + ENSURE_BITS(nbits); \ + (val) = PEEK_BITS_T(nbits); \ + REMOVE_BITS(nbits); \ +} while (0) +#endif + +#ifndef BITS_NO_READ_INPUT +# define READ_IF_NEEDED do { \ + if (i_ptr >= i_end) { \ + if (read_input(BITS_VAR)) \ + return BITS_VAR->error; \ + i_ptr = BITS_VAR->i_ptr; \ + i_end = BITS_VAR->i_end; \ + } \ +} while (0) + +static int read_input(BITS_TYPE *p) { + int read = p->sys->read(p->input, &p->inbuf[0], (int)p->inbuf_size); + if (read < 0) return p->error = MSPACK_ERR_READ; + + /* we might overrun the input stream by asking for bits we don't use, + * so fake 2 more bytes at the end of input */ + if (read == 0) { + if (p->input_end) { + D(("out of input bytes")) + return p->error = MSPACK_ERR_READ; + } + else { + read = 2; + p->inbuf[0] = p->inbuf[1] = 0; + p->input_end = 1; + } + } + + /* update i_ptr and i_end */ + p->i_ptr = &p->inbuf[0]; + p->i_end = &p->inbuf[read]; + return MSPACK_ERR_OK; +} +#endif +#endif |