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#include <bitfield/bitfield.h>
/**
* Find the ending bit of a bitfield within the final byte.
*
* Returns: a bit position from 0 to 7.
*/
int findEndBit(int startBit, int numBits) {
int endBit = (startBit + numBits) % 8;
return endBit == 0 ? 8 : endBit;
}
uint64_t bitmask(int numBits) {
return (((uint64_t)0x1) << numBits) - 1;
}
int startingByte(int startBit) {
return startBit / 8;
}
int endingByte(int startBit, int numBits) {
return (startBit + numBits - 1) / 8;
}
uint64_t getBitField(uint64_t data, int startBit, int numBits, bool bigEndian) {
int startByte = startingByte(startBit);
int endByte = endingByte(startBit, numBits);
if(!bigEndian) {
data = __builtin_bswap64(data);
}
uint8_t* bytes = (uint8_t*)&data;
uint64_t ret = bytes[startByte];
if(startByte != endByte) {
// The lowest byte address contains the most significant bit.
int i;
for(i = startByte + 1; i <= endByte; i++) {
ret = ret << 8;
ret = ret | bytes[i];
}
}
ret >>= 8 - findEndBit(startBit, numBits);
return ret & bitmask(numBits);
}
/**
* 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;
value <<= shiftDistance;
*data &= ~(bitmask(numBits) << shiftDistance);
*data |= value;
}
uint8_t nthByte(uint64_t source, int byteNum) {
return (source >> (64 - ((byteNum + 1) * 8))) & 0xFF;
}
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