105 lines
2.0 KiB
C
105 lines
2.0 KiB
C
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#include <assert.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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// stretchy buffers
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static size_t
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buf_len(void *buf)
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{
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return *(size_t *)(buf - (2 * sizeof(size_t)));
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}
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static void
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buf_set_len(void *buf, size_t len)
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{
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*(size_t *)(buf - (2 * sizeof(size_t))) = len;
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}
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static size_t
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buf_cap(void *buf)
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{
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return *(size_t *)(buf - sizeof(size_t));
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}
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static size_t
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buf_set_cap(void *buf, size_t cap)
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{
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*(size_t *)(buf - sizeof(size_t)) = cap;
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}
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static const size_t buf_overhead = 2 * sizeof(size_t);
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static void
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buf_allocate(void **buf, size_t nelem, size_t size)
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{
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size_t len = 0, cap = nelem * size;
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if (*buf == NULL) {
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*buf = malloc(buf_overhead + cap);
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*buf += buf_overhead;
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}
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else {
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len = buf_len(*buf);
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assert(len < cap);
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void *new_buf = malloc(buf_overhead + cap);
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new_buf += buf_overhead;
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memcpy(new_buf, *buf, cap);
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free(*buf);
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*buf = new_buf;
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}
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buf_set_len(*buf, len);
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buf_set_cap(*buf, cap);
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}
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static bool
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buf_must_grow(void *buf)
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{
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return (buf == NULL) || (buf_len(buf) == buf_cap(buf));
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}
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static const size_t buf_initial_length = 32;
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#define buf_push(buf, x) { \
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if ((void *)buf == NULL) { buf_allocate((void **)&(buf), buf_initial_length, sizeof((x))); } \
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if (buf_must_grow((void *)(buf))) { buf_allocate((void **)&(buf), 2 * buf_cap((void *)(buf)), 1); } \
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(buf)[buf_len((buf))] = (x); \
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buf_set_len((void *)(buf), buf_len((void *)(buf)) + 1); \
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} \
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static void
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buf_free(void *buf)
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{
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buf = (void *)buf - buf_overhead;
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free(buf);
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}
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/*
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* 1. NULL? → allocate with default size (32?)
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* 2.
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*/
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int
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main(int argc, char *argv[])
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{
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int *buf = NULL;
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buf_push(buf, 47); // std::vector::push_back
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// now buf actually points to a buffer
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buf_push(buf, 1234);
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printf("buf length: %lu / cap: %lu\n", buf_len(buf), buf_cap(buf));
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for (int i = 0; i < buf_len(buf); i++) {
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printf("%d\n", buf[i]);
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}
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for (int i = 0; i < 1024; i++) {
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buf_push(buf, i+1);
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}
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printf("buf length: %lu / cap: %lu\n", buf_len(buf), buf_cap(buf));
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buf_free(buf);
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return 0;
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}
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