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mirror of https://github.com/janet-lang/janet synced 2024-11-29 11:29:54 +00:00
janet/src/core/struct.c
Calvin Rose a87015598c Make janet_equals and janet_compare non recursive
This makes these operatios use constant stack space rather
than linear stackspace given the size of the inputs. This is important
to prevent certain parser input from causing a stack overflow - in
general, we try to avoid unbounded recursion.
2020-04-24 16:18:31 -05:00

170 lines
6.7 KiB
C

/*
* Copyright (c) 2020 Calvin Rose
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#ifndef JANET_AMALG
#include "features.h"
#include <janet.h>
#include "gc.h"
#include "util.h"
#include <math.h>
#endif
/* Begin creation of a struct */
JanetKV *janet_struct_begin(int32_t count) {
/* Calculate capacity as power of 2 after 2 * count. */
int32_t capacity = janet_tablen(2 * count);
if (capacity < 0) capacity = janet_tablen(count + 1);
size_t size = sizeof(JanetStructHead) + (size_t) capacity * sizeof(JanetKV);
JanetStructHead *head = janet_gcalloc(JANET_MEMORY_STRUCT, size);
head->length = count;
head->capacity = capacity;
head->hash = 0;
JanetKV *st = (JanetKV *)(head->data);
janet_memempty(st, capacity);
return st;
}
/* Find an item in a struct. Should be similar to janet_dict_find, but
* specialized to structs (slightly more compact). */
const JanetKV *janet_struct_find(const JanetKV *st, Janet key) {
int32_t cap = janet_struct_capacity(st);
int32_t index = janet_maphash(cap, janet_hash(key));
int32_t i;
for (i = index; i < cap; i++)
if (janet_checktype(st[i].key, JANET_NIL) || janet_equals(st[i].key, key))
return st + i;
for (i = 0; i < index; i++)
if (janet_checktype(st[i].key, JANET_NIL) || janet_equals(st[i].key, key))
return st + i;
return NULL;
}
/* Put a kv pair into a struct that has not yet been fully constructed.
* Nil keys and values are ignored, extra keys are ignore, and duplicate keys are
* ignored.
*
* Runs will be in sorted order, as the collisions resolver essentially
* preforms an in-place insertion sort. This ensures the internal structure of the
* hash map is independent of insertion order.
*/
void janet_struct_put(JanetKV *st, Janet key, Janet value) {
int32_t cap = janet_struct_capacity(st);
int32_t hash = janet_hash(key);
int32_t index = janet_maphash(cap, hash);
int32_t i, j, dist;
int32_t bounds[4] = {index, cap, 0, index};
if (janet_checktype(key, JANET_NIL) || janet_checktype(value, JANET_NIL)) return;
if (janet_checktype(key, JANET_NUMBER) && isnan(janet_unwrap_number(key))) return;
/* Avoid extra items */
if (janet_struct_hash(st) == janet_struct_length(st)) return;
for (dist = 0, j = 0; j < 4; j += 2)
for (i = bounds[j]; i < bounds[j + 1]; i++, dist++) {
int status;
int32_t otherhash;
int32_t otherindex, otherdist;
JanetKV *kv = st + i;
/* We found an empty slot, so just add key and value */
if (janet_checktype(kv->key, JANET_NIL)) {
kv->key = key;
kv->value = value;
/* Update the temporary count */
janet_struct_hash(st)++;
return;
}
/* Robinhood hashing - check if colliding kv pair
* is closer to their source than current. We use robinhood
* hashing to ensure that equivalent structs that are constructed
* with different order have the same internal layout, and therefor
* will compare properly - i.e., {1 2 3 4} should equal {3 4 1 2}.
* Collisions are resolved via an insertion sort insertion. */
otherhash = janet_hash(kv->key);
otherindex = janet_maphash(cap, otherhash);
otherdist = (i + cap - otherindex) & (cap - 1);
if (dist < otherdist)
status = -1;
else if (otherdist < dist)
status = 1;
else if (hash < otherhash)
status = -1;
else if (otherhash < hash)
status = 1;
else
status = janet_compare(key, kv->key);
/* If other is closer to their ideal slot */
if (status == 1) {
/* Swap current kv pair with pair in slot */
JanetKV temp = *kv;
kv->key = key;
kv->value = value;
key = temp.key;
value = temp.value;
/* Save dist and hash of new kv pair */
dist = otherdist;
hash = otherhash;
} else if (status == 0) {
/* A key was added to the struct more than once - replace old value */
kv->value = value;
return;
}
}
}
/* Finish building a struct */
const JanetKV *janet_struct_end(JanetKV *st) {
if (janet_struct_hash(st) != janet_struct_length(st)) {
/* Error building struct, probably duplicate values. We need to rebuild
* the struct using only the values that went in. The second creation should always
* succeed. */
JanetKV *newst = janet_struct_begin(janet_struct_hash(st));
for (int32_t i = 0; i < janet_struct_capacity(st); i++) {
JanetKV *kv = st + i;
if (!janet_checktype(kv->key, JANET_NIL)) {
janet_struct_put(newst, kv->key, kv->value);
}
}
st = newst;
}
janet_struct_hash(st) = janet_kv_calchash(st, janet_struct_capacity(st));
return (const JanetKV *)st;
}
/* Get an item from a struct */
Janet janet_struct_get(const JanetKV *st, Janet key) {
const JanetKV *kv = janet_struct_find(st, key);
return kv ? kv->value : janet_wrap_nil();
}
/* Convert struct to table */
JanetTable *janet_struct_to_table(const JanetKV *st) {
JanetTable *table = janet_table(janet_struct_capacity(st));
int32_t i;
for (i = 0; i < janet_struct_capacity(st); i++) {
const JanetKV *kv = st + i;
if (!janet_checktype(kv->key, JANET_NIL)) {
janet_table_put(table, kv->key, kv->value);
}
}
return table;
}