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add: reflect16

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rem:  swapbits, reflect
This commit is contained in:
iceman1001 2018-01-28 10:46:46 +01:00
commit cf44d04be1
2 changed files with 22 additions and 29 deletions
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43
armsrc/util.c
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@ -13,33 +13,28 @@ size_t nbytes(size_t nbits) {
return (nbits >> 3)+((nbits % 8) > 0); return (nbits >> 3)+((nbits % 8) > 0);
} }
// 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 < b; i++) {
newvalue ^= ((v >> i) & 1) << (b - 1 - i);
}
return newvalue;
}
uint8_t reflect8(uint8_t b) { uint8_t reflect8(uint8_t b) {
return ((b * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32; return ((b * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL >> 32;
} }
/* uint16_t reflect16(uint16_t b) {
ref http://www.csm.ornl.gov/~dunigan/crc.html uint16_t v = 0;
Returns the value v with the bottom b [0,32] bits reflected. v |= (b & 0x8000) >> 15;
Example: reflect(0x3e23L,3) == 0x3e26 v |= (b & 0x4000) >> 13;
*/ v |= (b & 0x2000) >> 11;
uint32_t reflect(uint32_t v, int b) { v |= (b & 0x1000) >> 9;
uint32_t t = v; v |= (b & 0x0800) >> 7;
for ( int i = 0; i < b; ++i) { v |= (b & 0x0400) >> 5;
if (t & 1) v |= (b & 0x0200) >> 3;
v |= BITMASK((b-1)-i); v |= (b & 0x0100) >> 1;
else
v &= ~BITMASK((b-1)-i); v |= (b & 0x0080) << 1;
t >>= 1; v |= (b & 0x0040) << 3;
} v |= (b & 0x0020) << 5;
v |= (b & 0x0010) << 7;
v |= (b & 0x0008) << 9;
v |= (b & 0x0004) << 11;
v |= (b & 0x0002) << 13;
v |= (b & 0x0001) << 15;
return v; return v;
} }

6
armsrc/util.h
View file

@ -40,11 +40,9 @@
#endif #endif
size_t nbytes(size_t nbits); size_t nbytes(size_t nbits);
uint32_t SwapBits(uint32_t value, int nrbits);
uint32_t reflect(uint32_t v, int b);
// dedicated 8bit reversal extern uint8_t reflect8(uint8_t b); // dedicated 8bit reversal
uint8_t reflect8(uint8_t b); extern uint16_t reflect16(uint16_t b); // dedicated 16bit reversal
void num_to_bytes(uint64_t n, size_t len, uint8_t* dest); void num_to_bytes(uint64_t n, size_t len, uint8_t* dest);
uint64_t bytes_to_num(uint8_t* src, size_t len); uint64_t bytes_to_num(uint8_t* src, size_t len);