98 lines
2.5 KiB
C
98 lines
2.5 KiB
C
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/* Copyright (c) 2015 Ryan Castellucci, All Rights Reserved */
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#include <unistd.h>
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#include <string.h>
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#include <fcntl.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <stdint.h>
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#include <arpa/inet.h> /* for ntohl/htonl */
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <sys/mman.h>
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#include "hex.h"
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#include "hash160.h"
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#include "hsearchf.h"
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#define HSEARCHF_DEBUG 0
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#define HASHLEN RIPEMD160_DIGEST_LENGTH
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#define RESULT(R) do { \
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res = R; \
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goto hsearchf_result; \
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} while (0)
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#define DO_MEMCMP(H) memcmp(H.uc, hash->uc, HASHLEN)
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// use fadvise to do a readbehind
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#define READ_AT(X, H) do { \
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posix_fadvise(fileno(f), ((X*HASHLEN)&0xfffff000)-4096, 8192, POSIX_FADV_WILLNEED); \
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if ((ret = fseek(f, X * HASHLEN, 0)) != 0) { return -1; } \
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if ((ret = fread(H.uc, HASHLEN, 1, f)) != 1) { return -1; } \
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++i; \
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} while (0)
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// interpolation search
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int hsearchf(FILE *f, hash160_t *hash) {
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int ret, res = 0, i = 0;
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size_t file_sz;
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struct stat sb;
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hash160_t low_h, mid_h, high_h;
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int64_t low_e, mid_e, high_e, entries;
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int64_t vlow, vhigh, vtarget;
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#if HSEARCHF_DEBUG > 0
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unsigned char hexed[64];
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#endif
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if ((ret = fstat(fileno(f), &sb)) != 0) { return -1; }
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file_sz = sb.st_size;
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entries = file_sz / HASHLEN;
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low_e = 0;
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high_e = entries - 1;
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vtarget = ntohl(hash->ul[0]);
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memset(low_h.uc, 0x00, HASHLEN);
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memset(high_h.uc, 0xff, HASHLEN);
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// this tries to minimize reads, but does a few extra comparisons
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while (low_e != high_e &&
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memcmp(hash->uc, low_h.uc, HASHLEN) > 0 &&
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memcmp(hash->uc, high_h.uc, HASHLEN) < 0) {
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vlow = ntohl(low_h.ul[0]); vhigh = ntohl(high_h.ul[0]);
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mid_e = low_e + (vtarget - vlow) * (high_e - low_e) / (vhigh - vlow);
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READ_AT(mid_e, mid_h);
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ret = DO_MEMCMP(mid_h);
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#if HSEARCHF_DEBUG > 1
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fprintf(stderr, "target %s checking %9jd %9jd %9jd",
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hex(hash->uc, HASHLEN, hexed, sizeof(hexed)), low_e, mid_e, high_e);
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fprintf(stderr, " got %s %11d %2d\n",
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hex(mid_h.uc, HASHLEN, hexed, sizeof(hexed)), ret, i);
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#endif
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if (ret == 0) {
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RESULT(1);
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} else if (ret < 0) {
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low_e = mid_e + 1;
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READ_AT(low_e, low_h);
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if (DO_MEMCMP(low_h) == 0) { RESULT(1); }
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} else { // ret > 0
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high_e = mid_e - 1;
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READ_AT(high_e, high_h);
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if (DO_MEMCMP(high_h) == 0) { RESULT(1); }
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}
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}
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hsearchf_result:
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#if HSEARCHF_DEBUG > 0
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fprintf(stderr, "target: %s reads: %3d result: %d\n", hex(hash->uc, HASHLEN, hexed, sizeof(hexed)), i, res);
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#endif
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return res;
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}
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/* vim: set ts=2 sw=2 et ai si: */
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