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add: fast 8bit reversal.

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iceman1001 2018-01-27 22:20:56 +01:00
commit ede55a1498
5 changed files with 22 additions and 9 deletions
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11
armsrc/util.c
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@ -13,14 +13,19 @@ size_t nbytes(size_t nbits) {
return (nbits >> 3)+((nbits % 8) > 0);
}
uint32_t SwapBits(uint32_t value, int nrbits) {
// Swap bit order on a uint32_t value. Can be limited by 'b' just use say 8 bits reversal
// note: function clears the rest of the bits.
uint32_t SwapBits(uint32_t v, int b) {
uint32_t newvalue = 0;
for(int i = 0; i < nrbits; i++) {
newvalue ^= ((value >> i) & 1) << (nrbits - 1 - i);
for(int i = 0; i < b; i++) {
newvalue ^= ((v >> i) & 1) << (b - 1 - i);
}
return newvalue;
}
uint8_t reflect8(uint8_t b) {
return ((b * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32;
}
/*
ref http://www.csm.ornl.gov/~dunigan/crc.html
Returns the value v with the bottom b [0,32] bits reflected.