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nnn/src/icons-hash.c
NRK fb5b2e5e64 icons-hash: fix bitwise rotation 
in case the rotation is 0, `v >> (32 - r)` would end up doing a 32 right
shift which is equal to the width of `v` and thus undefined behavior.

ref: https://blog.regehr.org/archives/1063
2023-01-03 02:20:21 +06:00

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/*
* simple program which outputs a hash-table of `icons_ext` with low collusion.
* the hash function is case-insensitive, it also doesn't hash beyond the
* length of the longest extension.
*/
#include <stddef.h>
#include <stdint.h>
#include <inttypes.h>
#define GOLDEN_RATIO_32 UINT32_C(2654442313) /* golden ratio for 32bits: (2^32) / 1.61803 */
#define GOLDEN_RATIO_64 UINT64_C(0x9E3793492EEDC3F7)
#define ICONS_TABLE_SIZE 8 /* size in bits. 8 = 256 */
#ifndef TOUPPER
#define TOUPPER(ch) (((ch) >= 'a' && (ch) <= 'z') ? ((ch) - 'a' + 'A') : (ch))
#endif
/* all of this is just for the static hash-table generation. only the hash
* function gets included in `nnn` binary.
*/
#ifdef ICONS_GENERATE
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include "icons.h"
#ifdef NDEBUG
#error "The hash-table generator relies on assert() to verify correctness."
#endif
#define ASSERT(X) assert(X)
#define ARRLEN(X) (sizeof(X) / sizeof((X)[0]))
#define MAX(A, B) ((A) > (B) ? (A) : (B))
#define HGEN_ITERARATION (1ul << 13)
#define ICONS_PROBE_MAX_ALLOWED 6
#define ICONS_MATCH_MAX (512)
#if 0 /* for logging some interesting info to stderr */
#define log(...) fprintf(stderr, "[INFO]: " __VA_ARGS__)
#else
#define log(...) ((void)0)
#endif
static uint32_t icon_ext_hash(const char *s);
/* change ICONS_TABLE_SIZE to increase the size of the table */
static struct icon_pair table[1u << ICONS_TABLE_SIZE];
static uint8_t seen[ARRLEN(table)];
/* arbitrarily picked starting position. change if needed.
* but ensure they're above 1 and prefer prime numbers.
*/
static uint32_t hash_start = 7;
static uint32_t hash_mul = 251; /* unused as of now */
/*
* use robin-hood insertion to reduce the max probe length
*/
static void
rh_insert(const struct icon_pair item, uint32_t idx, uint32_t n)
{
assert(n != 0);
for (uint32_t tries = 0; tries < ARRLEN(table); ++tries, ++n) {
if (seen[idx] < n) {
struct icon_pair tmp_item = table[idx];
uint32_t tmp_n = seen[idx];
assert(n < (uint8_t)-1);
table[idx] = item;
seen[idx] = n;
if (tmp_n != 0) /* the slot we inserted to wasn't empty */
rh_insert(tmp_item, idx, tmp_n);
return;
}
idx = (idx + 1) % ARRLEN(table);
}
assert(0); /* unreachable */
}
enum { PROBE_MAX, PROBE_TOTAL, PROBE_CNT };
static unsigned int *
table_populate(unsigned int p[static PROBE_CNT])
{
memset(seen, 0x0, sizeof seen);
memset(table, 0x0, sizeof table);
for (size_t i = 0; i < ARRLEN(icons_ext); ++i) {
if (icons_ext[i].icon[0] == '\0') /* skip empty entries */
continue;
uint32_t h = icon_ext_hash(icons_ext[i].match);
rh_insert(icons_ext[i], h, 1);
}
p[PROBE_MAX] = p[PROBE_TOTAL] = 0;
for (size_t i = 0; i < ARRLEN(seen); ++i) {
p[PROBE_MAX] = MAX(p[PROBE_MAX], seen[i]);
p[PROBE_TOTAL] += seen[i];
}
return p;
}
/* permuted congruential generator */
static uint32_t
pcg(uint64_t *state)
{
uint64_t oldstate = *state;
*state *= GOLDEN_RATIO_64;
uint32_t r = (oldstate >> 59);
uint32_t v = (oldstate ^ (oldstate >> 18)) >> 27;
return (v >> (-r & 31)) | (v << r);
}
int
main(void)
{
assert(ARRLEN(icons_ext) <= ARRLEN(table));
assert(ICONS_TABLE_SIZE < 16);
assert(1u << ICONS_TABLE_SIZE == ARRLEN(table));
assert((GOLDEN_RATIO_32 & 1) == 1); /* must be odd */
assert((GOLDEN_RATIO_64 & 1) == 1); /* must be odd */
assert(hash_start > 1);
assert(hash_mul > 1);
/* ensure power of 2 hashtable size which allows compiler to optimize
* away mod (`%`) operations
*/
assert((ARRLEN(table) & (ARRLEN(table) - 1)) == 0);
unsigned int max_probe = (unsigned)-1;
uint32_t best_hash_start = 0, best_hash_mul = 0, best_total_probe = 9999;
uint64_t hash_start_rng = hash_start, hash_mul_rng = hash_mul;
for (size_t i = 0; i < HGEN_ITERARATION; ++i) {
unsigned *p = table_populate((unsigned [PROBE_CNT]){0});
if (p[PROBE_MAX] < max_probe ||
(p[PROBE_MAX] == max_probe && p[PROBE_TOTAL] < best_total_probe))
{
max_probe = p[PROBE_MAX];
best_total_probe = p[PROBE_TOTAL];
best_hash_start = hash_start;
best_hash_mul = hash_mul;
}
hash_start = pcg(&hash_start_rng);
hash_mul = pcg(&hash_mul_rng);
}
assert(max_probe < ICONS_PROBE_MAX_ALLOWED);
hash_start = best_hash_start;
hash_mul = best_hash_mul;
{
unsigned *p = table_populate((unsigned [PROBE_CNT]){0});
assert(p[PROBE_MAX] == max_probe);
assert(p[PROBE_TOTAL] == best_total_probe);
}
/* sanity check */
double nitems = 0;
unsigned int total_probe = 0;
for (size_t i = 0; i < ARRLEN(icons_ext); ++i) {
if (icons_ext[i].icon[0] == 0)
continue;
uint32_t found = 0, h = icon_ext_hash(icons_ext[i].match);
for (uint32_t k = 0; k < max_probe; ++k) {
uint32_t z = (h + k) % ARRLEN(table);
++total_probe;
if (table[z].match && strcasecmp(icons_ext[i].match, table[z].match) == 0) {
found = 1;
break;
}
}
assert(found);
++nitems;
}
assert(total_probe == best_total_probe);
size_t match_max = 0, icon_max = 0;
for (size_t i = 0; i < ARRLEN(icons_name); ++i) {
match_max = MAX(match_max, strlen(icons_name[i].match) + 1);
icon_max = MAX(icon_max, strlen(icons_name[i].icon) + 1);
}
for (size_t i = 0; i < ARRLEN(icons_ext); ++i) {
match_max = MAX(match_max, strlen(icons_ext[i].match) + 1);
icon_max = MAX(icon_max, strlen(icons_ext[i].icon) + 1);
}
icon_max = MAX(icon_max, strlen(dir_icon.icon) + 1);
icon_max = MAX(icon_max, strlen(exec_icon.icon) + 1);
icon_max = MAX(icon_max, strlen(file_icon.icon) + 1);
assert(icon_max < ICONS_MATCH_MAX);
const char *uniq[ARRLEN(icons_ext)] = {0};
size_t uniq_head = 0;
for (size_t i = 0; i < ARRLEN(icons_ext); ++i) {
if (icons_ext[i].icon[0] == 0)
continue;
int isuniq = 1;
for (size_t k = 0; k < uniq_head; ++k) {
if (strcasecmp(uniq[k], icons_ext[i].icon) == 0) {
isuniq = 0;
break;
}
}
if (isuniq) {
assert(uniq_head < ARRLEN(uniq));
uniq[uniq_head++] = icons_ext[i].icon;
}
}
assert(uniq_head < (unsigned char)-1);
log("load-factor: %.2f (%u/%zu)\n", (nitems * 100.0) / (double)ARRLEN(table),
(unsigned int)nitems, ARRLEN(table));
log("max_probe : %6u\n", max_probe);
log("total_probe: %6u\n", total_probe);
log("uniq icons : %6zu\n", uniq_head);
log("no-compact : %6zu bytes\n", ARRLEN(table) * icon_max);
log("compaction : %6zu bytes\n", uniq_head * icon_max + ARRLEN(table));
log("hash_start : %6" PRIu32 "\n", hash_start);
log("hash_mul : %6" PRIu32 "\n", hash_mul);
printf("#ifndef INCLUDE_ICONS_GENERATED\n");
printf("#define INCLUDE_ICONS_GENERATED\n\n");
printf("/*\n * NOTE: This file is automatically generated.\n");
printf(" * DO NOT EDIT THIS FILE DIRECTLY.\n");
printf(" * Use `icons.h` to customize icons\n */\n\n");
printf("#define hash_start UINT32_C(%" PRIu32 ")\n", hash_start);
printf("#define hash_mul UINT32_C(%" PRIu32 ")\n\n", hash_mul);
printf("#define ICONS_PROBE_MAX %uu\n", max_probe);
printf("#define ICONS_MATCH_MAX %zuu\n\n", match_max);
printf("#define ICONS_STR_MAX %zuu\n\n", icon_max);
printf("struct icon_pair { const char match[ICONS_MATCH_MAX]; "
"const char icon[ICONS_STR_MAX]; unsigned char color; };\n\n");
printf("static const char icons_ext_uniq[%zu][ICONS_STR_MAX] = {\n", uniq_head);
for (size_t i = 0; i < uniq_head; ++i)
printf("\t\"%s\",\n", uniq[i]);
printf("};\n\n");
printf("static const struct {\n\tconst char match[ICONS_MATCH_MAX];\n"
"\tunsigned char idx;\n\tunsigned char color;\n} icons_ext[%zu] = {\n",
ARRLEN(table));
for (size_t i = 0; i < ARRLEN(table); ++i) {
if (table[i].icon == NULL || table[i].icon[0] == '\0') /* skip empty entries */
continue;
size_t k;
for (k = 0; k < uniq_head; ++k) {
if (strcasecmp(table[i].icon, uniq[k]) == 0)
break;
}
assert(k < uniq_head);
printf("\t[%3zu] = {\"%s\", %zu, %hhu },\n",
i, table[i].match, k, table[i].color);
}
printf("};\n\n");
printf("#endif /* INCLUDE_ICONS_GENERATED */\n");
}
#else
#define ASSERT(X) ((void)0)
#endif /* ICONS_GENERATE */
#if defined(ICONS_GENERATE) || defined(ICONS_ENABLED)
static uint32_t
icon_ext_hash(const char *str)
{
uint32_t i, hash = hash_start;
enum { wsz = sizeof hash * CHAR_BIT, z = wsz - ICONS_TABLE_SIZE, r = 5 };
/* just an xor-rotate hash. in general, this is a horrible hash
* function but for our specific input it works fine while being
* computationally cheap.
*/
for (i = 0; i < ICONS_MATCH_MAX && str[i] != '\0'; ++i) {
hash ^= TOUPPER((unsigned char)str[i]);
hash = (hash >> (wsz - r)) | (hash << r);
}
/* finalizer: https://probablydance.com/2018/06/16 */
hash ^= (hash >> z);
hash *= GOLDEN_RATIO_32;
hash >>= z;
ASSERT(hash < ARRLEN(table));
return hash;
}
#endif
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