ring_buffer.c

/* Code extrait de l'article Wikipedia Ring Buffer
   https://en.wikipedia.org/wiki/Circular_buffer
   consulté le 2014-12-16
   © Wikipedia, CC-BY-SA 3.0
*/

#include <stdlib.h>

/* Opaque buffer element type.  This would be defined by the application. */
typedef struct { int value; } ElemType;
 
/* Circular buffer object */
typedef struct {
    int         size;   /* maximum number of elements           */
    int         start;  /* index of oldest element              */
    int         end;    /* index at which to write new element  */
    ElemType   *elems;  /* vector of elements                   */
} CircularBuffer;
 
void cbInit(CircularBuffer *cb, int size) {
    cb->size  = size + 1; /* include empty elem */
    cb->start = 0;
    cb->end   = 0;
    cb->elems = calloc(cb->size, sizeof(ElemType));
}
 
void cbFree(CircularBuffer *cb) {
    free(cb->elems); /* OK if null */
}
 
int cbIsFull(CircularBuffer *cb) {
    return (cb->end + 1) % cb->size == cb->start;
}
 
int cbIsEmpty(CircularBuffer *cb) {
    return cb->end == cb->start;
}
 
/* Write an element, overwriting oldest element if buffer is full. App can
   choose to avoid the overwrite by checking cbIsFull(). */
void cbWrite(CircularBuffer *cb, ElemType *elem) {
    cb->elems[cb->end] = *elem;
    cb->end = (cb->end + 1) % cb->size;
    if (cb->end == cb->start)
        cb->start = (cb->start + 1) % cb->size; /* full, overwrite */
}
 
/* Read oldest element. App must ensure !cbIsEmpty() first. */
void cbRead(CircularBuffer *cb, ElemType *elem) {
    *elem = cb->elems[cb->start];
    cb->start = (cb->start + 1) % cb->size;
}
 
int main() {
    CircularBuffer cb;
    ElemType elem = {0};
 
    int testBufferSize = 10; /* arbitrary size */
    cbInit(&cb, testBufferSize);
 
    /* Fill buffer with test elements 3 times */
    for (elem.value = 0; elem.value < 3 * testBufferSize; ++ elem.value)
        cbWrite(&cb, &elem);
 
    /* Remove and print all elements */
    while (!cbIsEmpty(&cb)) {
        cbRead(&cb, &elem);
        Frama_C_show_each_elem(elem.value);
    }
 
    cbFree(&cb);
    return 0;
}

void* calloc(size_t nmemb, size_t size) {
  void* res = malloc(nmemb * size);
  if (res) {
    for(int i = 0; i<nmemb * size; i++) *((char*)res+i)=0;
  }
  return res;
}