circbuff.c

b/**
 * @file    circbuff.c 
 * @brief   A circular byte buffer implemtation optimized for UART  interfaces.
 *          Please note design for multiple instances of circular buffers. 
 *
 *
 */

#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>
#include "util/circbuff.h"
#include "mcu_assert.h"

void circ_buf_init(CIRCBUFF_T *c, uint8_t * const buffer, int pow2_size ) 
{

    assert_param (buffer != NULL);
    // check if number is a power of 2 
    // e.g. 0x100 & 0x0FF = 0 OK ,   0x120 & 0x11F = 0x100 assert
    assert_param (!(pow2_size & (pow2_size - 1))); 

    c->buffer = buffer;
    c->pow2_size = pow2_size;
    c->head = 0;
    c->tail = 0;

    return ;
}
 
inline int circ_buf_push(CIRCBUFF_T *c, uint8_t data)
{
    int retval = 0;

    // check if already full first
    if (  ((c->head+1) & (c->pow2_size-1)) == c->tail ) {
        // sorry, already full
        retval = -1;
    }
    else {
        // go ahead a write next 
        c->buffer[c->head] = data;
        // increment head, with wrap around
        c->head = (c->head+1) & (c->pow2_size-1);

        if ( (retval = (c->head - c->tail)) <= 0 )  {
            retval = c->pow2_size - c->tail + c->head;
        }
    } 
    return retval;
}

inline int circ_buf_pop(CIRCBUFF_T *c, uint8_t *data)
{
    int retval = 0;

    if (  c->tail == c->head ) {
        retval = 1;
        *data = 0;
    }
    else {

        *data = c->buffer[c->tail];
        // increment tail pointer with size mask
    	c->tail = (c->tail+1) & (c->pow2_size-1);
    } 

    return retval;
}