diff options
Diffstat (limited to 'src/d_huffman.c')
| -rw-r--r-- | src/d_huffman.c | 172 |
1 files changed, 172 insertions, 0 deletions
diff --git a/src/d_huffman.c b/src/d_huffman.c new file mode 100644 index 0000000..7431f98 --- /dev/null +++ b/src/d_huffman.c @@ -0,0 +1,172 @@ +#include <stdlib.h> +#include <stdio.h> + +#include "config.h" +#include "morecfg.h" + +#include "jpeglib.h" +#include "jpegint.h" + +#include "d_huffman.h" + + +/* + * Out-of-line code for bit fetching (shared with jdphuff.c). + * See jdhuff.h for info about usage. + * Note: current values of get_buffer and bits_left are passed as parameters, + * but are returned in the corresponding fields of the state struct. + * + * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width + * of get_buffer to be used. (On machines with wider words, an even larger + * buffer could be used.) However, on some machines 32-bit shifts are + * quite slow and take time proportional to the number of places shifted. + * (This is true with most PC compilers, for instance.) In this case it may + * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the + * average shift distance at the cost of more calls to jpeg_fill_bit_buffer. + */ + +#ifdef SLOW_SHIFT_32 +#define MIN_GET_BITS 15 /* minimum allowable value */ +#else +#define MIN_GET_BITS (BIT_BUF_SIZE-7) +#endif + +/* Load up the bit buffer to a depth of at least nbits */ +boolean jpeg_fill_bit_buffer(bitread_working_state *state, register bit_buf_type get_buffer, register int bits_left, int nbits) { + /* Copy heavily used state fields into locals (hopefully registers) */ + register const JOCTET * next_input_byte = state->next_input_byte; + register size_t bytes_in_buffer = state->bytes_in_buffer; + j_decompress_ptr cinfo = state->cinfo; + + /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ + /* (It is assumed that no request will be for more than that many bits.) */ + /* We fail to do so only if we hit a marker or are forced to suspend. */ + + if (cinfo->unread_marker == 0) { /* cannot advance past a marker */ + while (bits_left < MIN_GET_BITS) { + register int c; + + /* Attempt to read a byte */ + if (bytes_in_buffer == 0) { + if (! (*cinfo->src->fill_input_buffer) (cinfo)) { + return FALSE; + } + next_input_byte = cinfo->src->next_input_byte; + bytes_in_buffer = cinfo->src->bytes_in_buffer; + } + bytes_in_buffer--; + c = GETJOCTET(*next_input_byte++); + + /* If it's 0xFF, check and discard stuffed zero byte */ + if (c == 0xFF) { + /* Loop here to discard any padding FF's on terminating marker, + * so that we can save a valid unread_marker value. NOTE: we will + * accept multiple FF's followed by a 0 as meaning a single FF data + * byte. This data pattern is not valid according to the standard. + */ + do { + if (bytes_in_buffer == 0) { + if (! (*cinfo->src->fill_input_buffer) (cinfo)) { + return FALSE; + } + next_input_byte = cinfo->src->next_input_byte; + bytes_in_buffer = cinfo->src->bytes_in_buffer; + } + bytes_in_buffer--; + c = GETJOCTET(*next_input_byte++); + } while (c == 0xFF); + + if (c == 0) { + /* Found FF/00, which represents an FF data byte */ + c = 0xFF; + } else { + /* Oops, it's actually a marker indicating end of compressed data. + * Save the marker code for later use. + * Fine point: it might appear that we should save the marker into + * bitread working state, not straight into permanent state. But + * once we have hit a marker, we cannot need to suspend within the + * current MCU, because we will read no more bytes from the data + * source. So it is OK to update permanent state right away. + */ + cinfo->unread_marker = c; + /* See if we need to insert some fake zero bits. */ + goto no_more_bytes; + } + } + + /* OK, load c into get_buffer */ + get_buffer = (get_buffer << 8) | c; + bits_left += 8; + } /* end while */ + } else { + no_more_bytes: + /* We get here if we've read the marker that terminates the compressed + * data segment. There should be enough bits in the buffer register + * to satisfy the request; if so, no problem. + */ + if (nbits > bits_left) { + /* Uh-oh. Report corrupted data to user and stuff zeroes into + * the data stream, so that we can produce some kind of image. + * We use a nonvolatile flag to ensure that only one warning message + * appears per data segment. + */ + if (!cinfo->entropy->insufficient_data) { + perror("Corrupt JPEG data: premature end of data segment"); + /* WARNMS(cinfo, JWRN_HIT_MARKER); */ + cinfo->entropy->insufficient_data = TRUE; + } + /* Fill the buffer with zero bits */ + get_buffer <<= MIN_GET_BITS - bits_left; + bits_left = MIN_GET_BITS; + } + } + + /* Unload the local registers */ + state->next_input_byte = next_input_byte; + state->bytes_in_buffer = bytes_in_buffer; + state->get_buffer = get_buffer; + state->bits_left = bits_left; + + return TRUE; +} + + +/* + * Out-of-line code for Huffman code decoding. + * See jdhuff.h for info about usage. + */ + +int jpeg_huff_decode(bitread_working_state *state, register bit_buf_type get_buffer, register int bits_left, d_derived_tbl *htbl, int min_bits) { + register int l = min_bits; + register INT32 code; + + /* HUFF_DECODE has determined that the code is at least min_bits */ + /* bits long, so fetch that many bits in one swoop. */ + + CHECK_BIT_BUFFER(*state, l, return -1); + code = GET_BITS(l); + + /* Collect the rest of the Huffman code one bit at a time. */ + /* This is per Figure F.16 in the JPEG spec. */ + + while (code > htbl->maxcode[l]) { + code <<= 1; + CHECK_BIT_BUFFER(*state, 1, return -1); + code |= GET_BITS(1); + l++; + } + + /* Unload the local registers */ + state->get_buffer = get_buffer; + state->bits_left = bits_left; + + /* With garbage input we may reach the sentinel value l = 17. */ + + if (l > 16) { + perror("Corrupt JPEG data: bad Huffman code"); +/* WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); */ + return 0; /* fake a zero as the safest result */ + } + + return htbl->pub->huffval[ (int)(code + htbl->valoffset[l]) ]; +} |