ref: a920c765f2b4130590fb5971a50690b21664957a
dir: /libnandfs/hamming31_26.c/
#include "logfsos.h"
#include "logfs.h"
#include "nandfs.h"
static unsigned long row4 = 0x001fffc0;
static unsigned long row3 = 0x0fe03fc0;
static unsigned long row2 = 0x71e3c3c0;
static unsigned long row1 = 0xb66cccc0;
static unsigned long row0 = 0xdab55540;
static char map[] = {
-5, -4, 0, -3, 1, 2, 3, -2,
4, 5, 6, 7, 8, 9, 10, -1, 11,
12, 13, 14, 15, 16, 17, 18,
19, 20, 21, 22, 23, 24, 25,
};
#define mashbits(rown) \
c = (in) & (rown); \
c ^= c >> 16; \
c ^= c >> 8; \
c ^= c >> 4; \
c ^= c >> 2; \
c = (c ^ (c >> 1)) & 1; \
static uchar
_nandfshamming31_26calcparity(ulong in)
{
ulong c;
uchar out;
mashbits(row4); out = c;
mashbits(row3); out = (out << 1) | c;
mashbits(row2); out = (out << 1) | c;
mashbits(row1); out = (out << 1) | c;
mashbits(row0); out = (out << 1) | c;
return out;
}
ulong
_nandfshamming31_26calc(ulong in)
{
in &= 0xffffffc0;
return in | _nandfshamming31_26calcparity(in);
}
int
_nandfshamming31_26correct(ulong *in)
{
uchar eparity, parity;
ulong e;
eparity = _nandfshamming31_26calcparity(*in);
parity = (*in) & 0x1f;
e = eparity ^ parity;
if (e == 0)
return 0;
e--;
if (map[e] < 0)
return 1; // error in parity bits
e = map[e];
*in ^= 1 << (31 - e);
return 1;
}