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/*
* Copyright (C) 2007-2024 S[&]T, The Netherlands.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* 3. Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef CODA_READ_BITS_H
#define CODA_READ_BITS_H
#include "coda-read-bytes.h"
static int read_bits(coda_product *product, int64_t bit_offset, int64_t bit_length, uint8_t *dst)
{
unsigned long bit_shift;
int64_t padded_bit_length;
/* we read bits by treating them as big endian numbers.
* This means that
*
* src[0] | src[1]
* 7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
* . . a b c d e f|g h i j k . . .
*
* will be read and shifted to get
*
* dst[0] | dst[1]
* 7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
* . . . . . a b c|d e f g h i j k
*
* If the value is a number then on little endian machines the value needs to be converted to:
*
* dst[0] | dst[1]
* 7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
* d e f g h i j k|0 0 0 0 0 a b c
*
* Note that endian conversion does not happen within this function but happens in the functions that call
* read_bits().
*
* In theory we could also implement support for bitdata stored in lsb (least significant bit) to msb order.
* However, such a feature is currently NOT implemented!
* If we ever implement such a feature it should look like this:
* If the format of the source is (note the reverse order in which we display the bits!):
*
* src[0] | src[1]
* 0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7
* . . a b c d e f|g h i j k . . .
*
* then this will be read as
*
* tmp[0] | tmp[1]
* 7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
* f e d c b a . .|. . . k j i h g
*
* we can then perform a shift of bits (shifting 2 least significant bits from the right byte to the left byte)
* to get the little endian result
*
* dst[0] | dst[1]
* 7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
* h g f e d c b a|. . . . . k j i
*
* On big endian machines this can then be turned into a big endian number
*
* dst[0] | dst[1]
* 7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
* 0 0 0 0 0 k j i|h g f e d c b a
*/
/* The padded bit length is the number of 'padding' bits plus the bit length.
* The 'padding' bits are the bits between the start of byte (i.e. starting at the most significant bit) and the
* start of requested bits (in the (big endian) example above, bits 7 and 6 of src[0] are the padding bits).
*/
padded_bit_length = (bit_offset & 0x7) + bit_length;
bit_shift = (unsigned long)(-padded_bit_length & 0x7);
if (padded_bit_length <= 8)
{
/* all bits are located within a single byte, so we will use an optimized approach to extract the bits */
if (read_bytes(product, bit_offset >> 3, 1, dst) != 0)
{
return -1;
}
if (bit_shift != 0)
{
*dst >>= bit_shift;
}
if ((bit_length & 0x7) != 0)
{
*dst &= ((1 << bit_length) - 1);
}
}
else if (bit_shift == 0)
{
/* no shifting needed for the source bytes */
if (bit_length & 0x7)
{
unsigned long trailing_bit_length;
uint8_t buffer;
/* the first byte contains trailing bits and is not copied in full */
if (read_bytes(product, bit_offset >> 3, 1, &buffer) != 0)
{
return -1;
}
trailing_bit_length = (unsigned long)(bit_length & 0x7);
*dst = buffer & ((1 << trailing_bit_length) - 1);
dst++;
bit_offset += trailing_bit_length;
bit_length -= trailing_bit_length;
}
if (bit_length > 0)
{
/* use a plain copy for the remaining bytes */
if (read_bytes(product, bit_offset >> 3, bit_length >> 3, dst) != 0)
{
return -1;
}
}
}
else
{
uint8_t buffer[4];
union
{
uint8_t as_bytes[4];
uint32_t as_uint32;
} data;
/* we need to shift each byte */
/* we first copy the part modulo 24 bits (so the rest can be processed in chuncks of 24 bits each) */
if (bit_length % 24 != 0)
{
unsigned long mod24_bit_length;
unsigned long num_bytes_read;
unsigned long num_bytes_set;
unsigned long i;
mod24_bit_length = (unsigned long)(bit_length % 24);
num_bytes_read = bit_size_to_byte_size(((unsigned long)(bit_offset & 0x7)) + mod24_bit_length);
num_bytes_set = bit_size_to_byte_size(mod24_bit_length);
if (read_bytes(product, bit_offset >> 3, num_bytes_read, buffer) != 0)
{
return -1;
}
data.as_uint32 = 0;
for (i = 0; i < num_bytes_read; i++)
{
#ifdef WORDS_BIGENDIAN
data.as_bytes[i] = buffer[i];
#else
data.as_bytes[3 - i] = buffer[i];
#endif
}
data.as_uint32 = (data.as_uint32 >> (bit_shift + 8 * (4 - num_bytes_read))) & ((1 << mod24_bit_length) - 1);
for (i = 0; i < num_bytes_set; i++)
{
#ifdef WORDS_BIGENDIAN
dst[i] = data.as_bytes[(4 - num_bytes_set) + i];
#else
dst[i] = data.as_bytes[(num_bytes_set - 1) - i];
#endif
}
dst += num_bytes_set;
bit_offset += mod24_bit_length;
bit_length -= mod24_bit_length;
}
/* we copy the remaining data in chunks of 24 bits (3 bytes) at a time */
while (bit_length > 0)
{
#ifdef WORDS_BIGENDIAN
if (read_bytes(product, bit_offset >> 3, 4, data.as_bytes) != 0)
{
return -1;
}
data.as_uint32 >>= bit_shift;
dst[0] = data.as_bytes[1];
dst[1] = data.as_bytes[2];
dst[2] = data.as_bytes[3];
#else
if (read_bytes(product, bit_offset >> 3, 4, buffer) != 0)
{
return -1;
}
data.as_bytes[0] = buffer[3];
data.as_bytes[1] = buffer[2];
data.as_bytes[2] = buffer[1];
data.as_bytes[3] = buffer[0];
data.as_uint32 >>= bit_shift;
dst[0] = data.as_bytes[2];
dst[1] = data.as_bytes[1];
dst[2] = data.as_bytes[0];
#endif
dst += 3;
bit_offset += 24;
bit_length -= 24;
}
}
return 0;
}
#endif
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