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sketch.c
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sketch.c
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#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include "kvec.h"
#include "minimap.h"
unsigned char seq_nt4_table[256] = {
0, 1, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 0, 4, 1, 4, 4, 4, 2, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 0, 4, 1, 4, 4, 4, 2, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4
};
static inline uint64_t hash64(uint64_t key, uint64_t mask)
{
key = (~key + (key << 21)) & mask; // key = (key << 21) - key - 1;
key = key ^ key >> 24;
key = ((key + (key << 3)) + (key << 8)) & mask; // key * 265
key = key ^ key >> 14;
key = ((key + (key << 2)) + (key << 4)) & mask; // key * 21
key = key ^ key >> 28;
key = (key + (key << 31)) & mask;
return key;
}
/**
* Find symmetric (w,k)-minimizers on a DNA sequence
*
* @param str DNA sequence
* @param len length of $str
* @param w find a minimizer for every $w consecutive k-mers
* @param k k-mer size
* @param rid reference ID; will be copied to the output $p array
* @param p minimizers; p->a[i].x is the 2k-bit hash value;
* p->a[i].y = rid<<32 | lastPos<<1 | strand
* where lastPos is the position of the last base of the i-th minimizer,
* and strand indicates whether the minimizer comes from the top or the bottom strand.
* Callers may want to set "p->n = 0"; otherwise results are appended to p
*/
void mm_sketch(const char *str, int len, int w, int k, uint32_t rid, mm128_v *p)
{
uint64_t shift1 = 2 * (k - 1), mask = (1ULL<<2*k) - 1, kmer[2] = {0,0};
int i, j, l, buf_pos, min_pos;
mm128_t *buf, min = { UINT64_MAX, UINT64_MAX };
assert(len > 0 && w > 0 && k > 0);
buf = (mm128_t*)alloca(w * 16);
memset(buf, 0xff, w * 16);
for (i = l = buf_pos = min_pos = 0; i < len; ++i) {
int c = seq_nt4_table[(uint8_t)str[i]];
mm128_t info = { UINT64_MAX, UINT64_MAX };
if (c < 4) { // not an ambiguous base
int z;
kmer[0] = (kmer[0] << 2 | c) & mask; // forward k-mer
kmer[1] = (kmer[1] >> 2) | (3ULL^c) << shift1; // reverse k-mer
if (kmer[0] == kmer[1]) continue; // skip "symmetric k-mers" as we don't know it strand
z = kmer[0] < kmer[1]? 0 : 1; // strand
if (++l >= k)
info.x = hash64(kmer[z], mask), info.y = (uint64_t)rid<<32 | (uint32_t)i<<1 | z;
} else l = 0;
buf[buf_pos] = info; // need to do this here as appropriate buf_pos and buf[buf_pos] are needed below
if (l == w + k - 1) { // special case for the first window - because identical k-mers are not stored yet
for (j = buf_pos + 1; j < w; ++j)
if (min.x == buf[j].x && buf[j].y != min.y) kv_push(mm128_t, *p, buf[j]);
for (j = 0; j < buf_pos; ++j)
if (min.x == buf[j].x && buf[j].y != min.y) kv_push(mm128_t, *p, buf[j]);
}
if (info.x <= min.x) { // a new minimum; then write the old min
if (l >= w + k) kv_push(mm128_t, *p, min);
min = info, min_pos = buf_pos;
} else if (buf_pos == min_pos) { // old min has moved outside the window
if (l >= w + k - 1) kv_push(mm128_t, *p, min);
for (j = buf_pos + 1, min.x = UINT64_MAX; j < w; ++j) // the two loops are necessary when there are identical k-mers
if (min.x >= buf[j].x) min = buf[j], min_pos = j; // >= is important s.t. min is always the closest k-mer
for (j = 0; j <= buf_pos; ++j)
if (min.x >= buf[j].x) min = buf[j], min_pos = j;
if (l >= w + k - 1) { // write identical k-mers
for (j = buf_pos + 1; j < w; ++j) // these two loops make sure the output is sorted
if (min.x == buf[j].x && min.y != buf[j].y) kv_push(mm128_t, *p, buf[j]);
for (j = 0; j <= buf_pos; ++j)
if (min.x == buf[j].x && min.y != buf[j].y) kv_push(mm128_t, *p, buf[j]);
}
}
if (++buf_pos == w) buf_pos = 0;
}
if (min.x != UINT64_MAX)
kv_push(mm128_t, *p, min);
}