ion: start implementing stretchy buffers via the video.

This commit is contained in:
Kyle Isom 2018-03-15 15:53:22 -07:00
parent 39937b6c00
commit d67ca84c45
3 changed files with 35 additions and 69 deletions

View File

@ -1,3 +1,8 @@
{
"cppcheck.includePaths": ["${workspaceRoot}/ods/src"]
"cppcheck.includePaths": [
"${workspaceRoot}/ods/src"
],
"files.associations": {
"*.ipp": "c"
}
}

View File

@ -1,6 +1,6 @@
TARGET := ion
OBJS := $(TARGET).o
CFLAGS := -g
CFLAGS := -g -std=c99
all: $(TARGET)

View File

@ -4,84 +4,43 @@
#include <stdlib.h>
#include <string.h>
#define MAX(a, b) a < b ? b : a
// stretchy buffers
static size_t
buf_len(void *buf)
{
return *(size_t *)(buf - (2 * sizeof(size_t)));
}
typedef struct _BufHeader {
size_t len;
size_t cap;
char buf[0]; // C99
} BufHeader;
static void
buf_set_len(void *buf, size_t len)
{
*(size_t *)(buf - (2 * sizeof(size_t))) = len;
}
#define buf__hdr(b) (BufHeader *)((char *)buf - offsetof(BufHeader, buf))
#define buf_fits(b, n) ((buf_len(b) + n) <= buf_cap(b))
#define buf__fit(b, n) (buf__fits(b, n) ? 0 : (b) = (buf_grow(b, 2*buf_cap(b), sizeof(*b))))
static size_t
buf_cap(void *buf)
{
return *(size_t *)(buf - sizeof(size_t));
}
#define buf_len(b) ((b) ? buf__hdr(b)->len : 0)
#define buf_cap(b) ((b) ? buf__hdr(b)->cap : 0)
#define buf_push(b, x) (buf__fit((b), 1), (b)[buf_len(b)++] = (x))
static size_t
buf_set_cap(void *buf, size_t cap)
void *
buf__grow(const void *buf, size_t nlen, size_t esize)
{
*(size_t *)(buf - sizeof(size_t)) = cap;
}
size_t ncap = MAX(1 + 2*buf_cap(buf), new_len);
assert(nlen <= ncap);
size_t nsize = ncap * esize;
BufHdr *nhdr;
static const size_t buf_overhead = 2 * sizeof(size_t);
static void
buf_allocate(void **buf, size_t nelem, size_t size)
{
size_t len = 0, cap = nelem * size;
if (*buf == NULL) {
*buf = malloc(buf_overhead + cap);
*buf += buf_overhead;
if (buf) {
nhdr = realloc(buf__hdr(buf), nsize)
}
else {
len = buf_len(*buf);
assert(len < cap);
void *new_buf = malloc(buf_overhead + cap);
new_buf += buf_overhead;
memcpy(new_buf, *buf, cap);
free(*buf);
*buf = new_buf;
nhdr = malloc(new_size)
nhdr->len = 0;
}
buf_set_len(*buf, len);
buf_set_cap(*buf, cap);
nhdr.cap = ncap;
return nhdr;
}
static bool
buf_must_grow(void *buf)
{
return (buf == NULL) || (buf_len(buf) == buf_cap(buf));
}
static const size_t buf_initial_length = 32;
#define buf_push(buf, x) { \
if ((void *)buf == NULL) { buf_allocate((void **)&(buf), buf_initial_length, sizeof((x))); } \
if (buf_must_grow((void *)(buf))) { buf_allocate((void **)&(buf), 2 * buf_cap((void *)(buf)), 1); } \
(buf)[buf_len((buf))] = (x); \
buf_set_len((void *)(buf), buf_len((void *)(buf)) + 1); \
} \
static void
buf_free(void *buf)
{
buf = (void *)buf - buf_overhead;
free(buf);
}
/*
* 1. NULL? allocate with default size (32?)
* 2.
*/
int
main(int argc, char *argv[])
{
@ -90,7 +49,9 @@ main(int argc, char *argv[])
// now buf actually points to a buffer
buf_push(buf, 1234);
printf("buf length: %lu / cap: %lu\n", buf_len(buf), buf_cap(buf));
printf("buf length: %lu / cap: %lu\n",
(unsigned long)buf_len(buf),
(unsigned long)buf_cap(buf));
for (int i = 0; i < buf_len(buf); i++) {
printf("%d\n", buf[i]);
}