diff options
Diffstat (limited to 'src/bitfield/bitfield.c')
| -rw-r--r-- | src/bitfield/bitfield.c | 167 |
1 files changed, 23 insertions, 144 deletions
diff --git a/src/bitfield/bitfield.c b/src/bitfield/bitfield.c index 834e443e..b0396413 100644 --- a/src/bitfield/bitfield.c +++ b/src/bitfield/bitfield.c @@ -5,124 +5,16 @@ #define NIBBLE_SIZE (CHAR_BIT / 2) -#define PREPARE_FIRST_COPY() \ - do { \ - if (source_length >= (CHAR_BIT - destination_offset_modulo)) { \ - *destination &= reverse_mask[destination_offset_modulo]; \ - source_length -= CHAR_BIT - destination_offset_modulo; \ - } else { \ - *destination &= reverse_mask[destination_offset_modulo] \ - | reverse_mask_xor[destination_offset_modulo + source_length + 1];\ - c &= reverse_mask[destination_offset_modulo + source_length ];\ - source_length = 0; \ - } } while (0) - -/** - * Find the ending bit of a bitfield within the final byte. - * - * Returns: a bit position from 0 to 7. - */ -static uint8_t findEndBit(const uint16_t startBit, const uint16_t numBits) { - int endBit = numBits % CHAR_BIT; - return endBit == 0 ? CHAR_BIT : endBit; -} - - -// TODO can probably remove this -static int byteForBit(const uint16_t startBit) { - return startBit / CHAR_BIT; +uint64_t bitmask(const uint8_t numBits) { + return (((uint64_t)0x1) << numBits) - 1; } -/* Thanks to - * http://stackoverflow.com/questions/3534535/whats-a-time-efficient-algorithm-to-copy-unaligned-bit-arrays - */ -static void bitarray_copy(const uint8_t* source_origin, int source_offset, - int source_length, uint8_t* destination_origin, int destination_offset) { - static const uint8_t reverse_mask[] = - { 0x55, 0x80, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc, 0xfe, 0xff }; - static const uint8_t reverse_mask_xor[] = - { 0xff, 0x7f, 0x3f, 0x1f, 0x0f, 0x07, 0x03, 0x01, 0x00 }; - - if(source_length < 1) { - return; - } - - const uint8_t* source = source_origin + byteForBit(source_offset); - uint8_t* destination = destination_origin + byteForBit(destination_offset); - int source_offset_modulo = source_offset % CHAR_BIT; - int destination_offset_modulo = destination_offset % CHAR_BIT; - - if(source_offset_modulo == destination_offset_modulo) { - if(source_offset_modulo > 0) { - uint8_t c = reverse_mask_xor[destination_offset_modulo] & *source++; - PREPARE_FIRST_COPY(); - *destination++ |= c; - } - - int byte_len = source_length / CHAR_BIT; - int source_length_modulo = source_length % CHAR_BIT; - - if(byte_len > 0) { - memcpy(destination, source, byte_len); - source += byte_len; - destination += byte_len; - } - - if(source_length_modulo > 0) { - *destination &= reverse_mask_xor[source_length_modulo]; - *destination |= reverse_mask[source_length_modulo] & *source; - } - } else { - int bit_diff_left_shift; - int bit_diff_right_shift; - uint8_t c; - /* - * Begin: Line things up on destination. - */ - if(source_offset_modulo > destination_offset_modulo) { - bit_diff_left_shift = source_offset_modulo - destination_offset_modulo; - bit_diff_right_shift = CHAR_BIT - bit_diff_left_shift; - - c = *source++ << bit_diff_left_shift; - c |= *source >> bit_diff_right_shift; - c &= reverse_mask_xor[destination_offset_modulo]; - } else { - bit_diff_right_shift = destination_offset_modulo - source_offset_modulo; - bit_diff_left_shift = CHAR_BIT - bit_diff_right_shift; - - c = *source >> bit_diff_right_shift & - reverse_mask_xor[destination_offset_modulo]; - } - PREPARE_FIRST_COPY(); - *destination++ |= c; - - /* - * Middle: copy with only shifting the source. - */ - int byte_len = source_length / CHAR_BIT; - while(--byte_len >= 0) { - c = *source++ << bit_diff_left_shift; - c |= *source >> bit_diff_right_shift; - *destination++ = c; - } - - /* - * End: copy the remaing bits; - */ - int source_length_modulo = source_length % CHAR_BIT; - if(source_length_modulo > 0) { - c = *source++ << bit_diff_left_shift; - c |= *source >> bit_diff_right_shift; - c &= reverse_mask[source_length_modulo]; - - *destination &= reverse_mask_xor[source_length_modulo]; - *destination |= c; - } +static uint16_t bitsToBytes(uint32_t bits) { + uint8_t byte_count = bits / CHAR_BIT; + if(bits % CHAR_BIT != 0) { + ++byte_count; } -} - -uint64_t bitmask(const uint8_t numBits) { - return (((uint64_t)0x1) << numBits) - 1; + return byte_count; } uint64_t getBitField(uint64_t data, const uint16_t startBit, @@ -131,24 +23,18 @@ uint64_t getBitField(uint64_t data, const uint16_t startBit, if(!bigEndian) { data = __builtin_bswap64(data); } - getBits(startBit, numBits, (const uint8_t*)&data, - CHAR_BIT * sizeof(uint64_t), - bigEndian ? ENDIANNESS_BIG_ENDIAN : ENDIANNESS_LITTLE_ENDIAN, - result); - // TODO the result has already been shifted to be aligned right, so if we - // try and bswap here it's going to be screwed up unless it was byte aligned + copyBitsRightAligned((const uint8_t*)&data, sizeof(data), startBit, numBits, + result, sizeof(result)); uint64_t int_result = 0; - // TODO should the API return the byte length of data in the result array? - // i think yes. - uint8_t byte_count = numBits / CHAR_BIT; - if(numBits % CHAR_BIT != 0) { - ++byte_count; - } - // TODO wow, can't believe this works, but something is clearly wrong with - // the API! - for(int i = 0; i < byte_count; i++) { - int_result |= result[byte_count - i - 1] << (CHAR_BIT * i); + if(!bigEndian) { + // we need to swap the byte order of the array to get it into a + // uint64_t, but it's been right aligned so we have to be more careful + for(int i = 0; i < bitsToBytes(numBits); i++) { + int_result |= result[bitsToBytes(numBits) - i - 1] << (CHAR_BIT * i); + } + } else { + int_result = *(uint64_t*)result; } return int_result; } @@ -157,19 +43,20 @@ uint64_t getBitField(uint64_t data, const uint16_t startBit, * TODO it would be nice to have a warning if you call with this a value that * won't fit in the number of bits you've specified it should use. */ -void setBitField(uint64_t* data, uint64_t value, int startBit, int numBits) { - int shiftDistance = 64 - startBit - numBits; +void setBitField(uint64_t* data, uint64_t value, const uint16_t startPos, + const uint16_t numBits) { + int shiftDistance = 64 - startPos - numBits; value <<= shiftDistance; *data &= ~(bitmask(numBits) << shiftDistance); *data |= value; } -uint8_t nthByte(uint64_t source, int byteNum) { +uint8_t nthByte(const uint64_t source, const uint16_t byteNum) { return (source >> (64 - ((byteNum + 1) * CHAR_BIT))) & 0xFF; } uint8_t getNibble(const uint8_t nibble_index, const uint8_t data[], - const uint8_t length, Endianness endianness) { + const uint8_t length) { uint8_t byte_index = nibble_index / 2; uint8_t result; if(byte_index < length) { @@ -182,18 +69,10 @@ uint8_t getNibble(const uint8_t nibble_index, const uint8_t data[], return result; } -// TODO getBytes, return status and store in output parameter uint8_t getByte(const uint8_t byte_index, const uint8_t data[], - const uint8_t length, Endianness endianness) { + const uint8_t length) { if(byte_index < length) { return data[byte_index]; } return 0; } - -void getBits(const uint16_t start_index, const uint16_t field_size, - const uint8_t data[], const uint8_t length, Endianness endianness, - uint8_t* result) { - bitarray_copy(data, start_index, field_size, result, - CHAR_BIT - findEndBit(start_index, field_size)); -} |