/*
* Needed since we store all the parity at the end of the word, not at the expected
- * power-of-two bit positions. This is the inverse of the mapping
- * (0..31) -> (0, 16, 8, 4, 2, 1, the rest in ascending order)
+ * power-of-two bit positions.
*/
unsigned char permutation_table[CODE_BITS] = {
- 0, 5, 4, 6, 3, 7, 8, 9, 2, 10, 11, 12, 13, 14, 15, 16, 1, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31
+ 0, 5, 4, 31, 3, 30, 29, 28, 2, 27, 26, 25, 24, 23, 22, 21, 1, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6
};
/* FIXME: check if the lookup table actually helps us any here */
return 1;
}
-#if 0
/* Correct any single-bit error -- assumes there are no double-bit errors */
unsigned correct_single_bit_error(unsigned code)
{
- unsigned bits[CODE_BITS];
- unsigned parity[PARITY_BITS];
- unsigned i, bp = 0;
+ unsigned parity_diff = generate_parity(code >> PARITY_BITS) ^ code;
+ unsigned bp = 0, i;
- parity[EXTRA_BIT_POSITION] = 0;
-
- for (i = 0; i < CODE_BITS; ++i) {
- bits[i] = (code & (1 << i)) ? 1 : 0;
- }
- for (i = 1; i < CODE_BITS; ++i) {
- parity[EXTRA_BIT_POSITION] ^= bits[i];
- }
-
- parity[0] = bits[PARITY_BITS+0] ^ bits[PARITY_BITS+1] ^ bits[PARITY_BITS+3] ^ bits[PARITY_BITS+4] ^ bits[PARITY_BITS+6] ^ bits[PARITY_BITS+8] ^ bits[PARITY_BITS+10];
- parity[1] = bits[PARITY_BITS+0] ^ bits[PARITY_BITS+2] ^ bits[PARITY_BITS+3] ^ bits[PARITY_BITS+5] ^ bits[PARITY_BITS+6] ^ bits[PARITY_BITS+9] ^ bits[PARITY_BITS+10];
- parity[2] = bits[PARITY_BITS+1] ^ bits[PARITY_BITS+2] ^ bits[PARITY_BITS+3] ^ bits[PARITY_BITS+7] ^ bits[PARITY_BITS+8] ^ bits[PARITY_BITS+9] ^ bits[PARITY_BITS+10];
- parity[3] = bits[PARITY_BITS+4] ^ bits[PARITY_BITS+5] ^ bits[PARITY_BITS+6] ^ bits[PARITY_BITS+7] ^ bits[PARITY_BITS+8] ^ bits[PARITY_BITS+9] ^ bits[PARITY_BITS+10];
-
for (i = 0; i < PARITY_BITS - 1; ++i) {
- if (parity[i] != bits[PARITY_BITS - 1 - i]) {
+ if (parity_diff & (1 << (PARITY_BITS - 1 - i))) {
bp |= (1 << i);
}
}
if (bp != 0) {
/* flip the wrong bit */
code ^= (1 << permutation_table[bp]);
- parity[EXTRA_BIT_POSITION] ^= 1;
}
/* recompute the lower parity */
- return (code & ~1) | parity[EXTRA_BIT_POSITION];
+ return (code & ~1) | find_parity_32(code & ~1);
}
-#endif
void check_zero_bit_detection()
{
if (has_double_error(corrupted_code)) {
printf("ERROR: Failed single-bit test 2 for %x with bit %u flipped\n", i, j);
}
-#if 0
if (correct_single_bit_error(corrupted_code) != code) {
printf("ERROR: Failed single-bit correction test for %x with bit %u flipped\n", i, j);
}
-#endif
}
}
}