in nand/ecc-sw-hamming.c [115:353]
int ecc_sw_hamming_calculate(const unsigned char *buf, unsigned int step_size,
unsigned char *code, bool sm_order)
{
const u32 *bp = (uint32_t *)buf;
const u32 eccsize_mult = (step_size == 256) ? 1 : 2;
/* current value in buffer */
u32 cur;
/* rp0..rp17 are the various accumulated parities (per byte) */
u32 rp0, rp1, rp2, rp3, rp4, rp5, rp6, rp7, rp8, rp9, rp10, rp11, rp12,
rp13, rp14, rp15, rp16, rp17;
/* Cumulative parity for all data */
u32 par;
/* Cumulative parity at the end of the loop (rp12, rp14, rp16) */
u32 tmppar;
int i;
par = 0;
rp4 = 0;
rp6 = 0;
rp8 = 0;
rp10 = 0;
rp12 = 0;
rp14 = 0;
rp16 = 0;
rp17 = 0;
/*
* The loop is unrolled a number of times;
* This avoids if statements to decide on which rp value to update
* Also we process the data by longwords.
* Note: passing unaligned data might give a performance penalty.
* It is assumed that the buffers are aligned.
* tmppar is the cumulative sum of this iteration.
* needed for calculating rp12, rp14, rp16 and par
* also used as a performance improvement for rp6, rp8 and rp10
*/
for (i = 0; i < eccsize_mult << 2; i++) {
cur = *bp++;
tmppar = cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= tmppar;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp8 ^= tmppar;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp10 ^= tmppar;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp6 ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp8 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp6 ^= cur;
cur = *bp++;
tmppar ^= cur;
rp4 ^= cur;
cur = *bp++;
tmppar ^= cur;
par ^= tmppar;
if ((i & 0x1) == 0)
rp12 ^= tmppar;
if ((i & 0x2) == 0)
rp14 ^= tmppar;
if (eccsize_mult == 2 && (i & 0x4) == 0)
rp16 ^= tmppar;
}
/*
* handle the fact that we use longword operations
* we'll bring rp4..rp14..rp16 back to single byte entities by
* shifting and xoring first fold the upper and lower 16 bits,
* then the upper and lower 8 bits.
*/
rp4 ^= (rp4 >> 16);
rp4 ^= (rp4 >> 8);
rp4 &= 0xff;
rp6 ^= (rp6 >> 16);
rp6 ^= (rp6 >> 8);
rp6 &= 0xff;
rp8 ^= (rp8 >> 16);
rp8 ^= (rp8 >> 8);
rp8 &= 0xff;
rp10 ^= (rp10 >> 16);
rp10 ^= (rp10 >> 8);
rp10 &= 0xff;
rp12 ^= (rp12 >> 16);
rp12 ^= (rp12 >> 8);
rp12 &= 0xff;
rp14 ^= (rp14 >> 16);
rp14 ^= (rp14 >> 8);
rp14 &= 0xff;
if (eccsize_mult == 2) {
rp16 ^= (rp16 >> 16);
rp16 ^= (rp16 >> 8);
rp16 &= 0xff;
}
/*
* we also need to calculate the row parity for rp0..rp3
* This is present in par, because par is now
* rp3 rp3 rp2 rp2 in little endian and
* rp2 rp2 rp3 rp3 in big endian
* as well as
* rp1 rp0 rp1 rp0 in little endian and
* rp0 rp1 rp0 rp1 in big endian
* First calculate rp2 and rp3
*/
#ifdef __BIG_ENDIAN
rp2 = (par >> 16);
rp2 ^= (rp2 >> 8);
rp2 &= 0xff;
rp3 = par & 0xffff;
rp3 ^= (rp3 >> 8);
rp3 &= 0xff;
#else
rp3 = (par >> 16);
rp3 ^= (rp3 >> 8);
rp3 &= 0xff;
rp2 = par & 0xffff;
rp2 ^= (rp2 >> 8);
rp2 &= 0xff;
#endif
/* reduce par to 16 bits then calculate rp1 and rp0 */
par ^= (par >> 16);
#ifdef __BIG_ENDIAN
rp0 = (par >> 8) & 0xff;
rp1 = (par & 0xff);
#else
rp1 = (par >> 8) & 0xff;
rp0 = (par & 0xff);
#endif
/* finally reduce par to 8 bits */
par ^= (par >> 8);
par &= 0xff;
/*
* and calculate rp5..rp15..rp17
* note that par = rp4 ^ rp5 and due to the commutative property
* of the ^ operator we can say:
* rp5 = (par ^ rp4);
* The & 0xff seems superfluous, but benchmarking learned that
* leaving it out gives slightly worse results. No idea why, probably
* it has to do with the way the pipeline in pentium is organized.
*/
rp5 = (par ^ rp4) & 0xff;
rp7 = (par ^ rp6) & 0xff;
rp9 = (par ^ rp8) & 0xff;
rp11 = (par ^ rp10) & 0xff;
rp13 = (par ^ rp12) & 0xff;
rp15 = (par ^ rp14) & 0xff;
if (eccsize_mult == 2)
rp17 = (par ^ rp16) & 0xff;
/*
* Finally calculate the ECC bits.
* Again here it might seem that there are performance optimisations
* possible, but benchmarks showed that on the system this is developed
* the code below is the fastest
*/
if (sm_order) {
code[0] = (invparity[rp7] << 7) | (invparity[rp6] << 6) |
(invparity[rp5] << 5) | (invparity[rp4] << 4) |
(invparity[rp3] << 3) | (invparity[rp2] << 2) |
(invparity[rp1] << 1) | (invparity[rp0]);
code[1] = (invparity[rp15] << 7) | (invparity[rp14] << 6) |
(invparity[rp13] << 5) | (invparity[rp12] << 4) |
(invparity[rp11] << 3) | (invparity[rp10] << 2) |
(invparity[rp9] << 1) | (invparity[rp8]);
} else {
code[1] = (invparity[rp7] << 7) | (invparity[rp6] << 6) |
(invparity[rp5] << 5) | (invparity[rp4] << 4) |
(invparity[rp3] << 3) | (invparity[rp2] << 2) |
(invparity[rp1] << 1) | (invparity[rp0]);
code[0] = (invparity[rp15] << 7) | (invparity[rp14] << 6) |
(invparity[rp13] << 5) | (invparity[rp12] << 4) |
(invparity[rp11] << 3) | (invparity[rp10] << 2) |
(invparity[rp9] << 1) | (invparity[rp8]);
}
if (eccsize_mult == 1)
code[2] =
(invparity[par & 0xf0] << 7) |
(invparity[par & 0x0f] << 6) |
(invparity[par & 0xcc] << 5) |
(invparity[par & 0x33] << 4) |
(invparity[par & 0xaa] << 3) |
(invparity[par & 0x55] << 2) |
3;
else
code[2] =
(invparity[par & 0xf0] << 7) |
(invparity[par & 0x0f] << 6) |
(invparity[par & 0xcc] << 5) |
(invparity[par & 0x33] << 4) |
(invparity[par & 0xaa] << 3) |
(invparity[par & 0x55] << 2) |
(invparity[rp17] << 1) |
(invparity[rp16] << 0);
return 0;
}