ref: 7975eec3e602fd5bc3e93c78f4166259190f2fe9
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; }