spsc.h

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#ifndef SPSC_H
#define SPSC_H
 
#include <stdint.h>
#include <string.h>
 
#if defined(__arm__)
#define SPSC_BARRIER() __asm volatile ("dmb" ::: "memory")
#else
#define SPSC_BARRIER() __sync_synchronize()
#endif
 
typedef struct {
    volatile uint32_t head;      
    volatile uint32_t tail;      
    uint32_t          mask;      
    uint32_t          item;      
    uint8_t          *buf;
} spsc_t;
 
#define SPSC_DEFINE(name, type, n)                                          \
    static uint8_t name##_buf[(n) * sizeof(type)];                          \
    static spsc_t  name = { 0u, 0u, (n) - 1u, sizeof(type), name##_buf }
 
static inline void spsc_reset(spsc_t *q) { q->head = q->tail = 0u; }
 
static inline int spsc_push(spsc_t *q, const void *it)
{
    const uint32_t h = q->head;
    if (h - q->tail > q->mask) return -1;                 
    memcpy(&q->buf[(h & q->mask) * q->item], it, q->item);
    SPSC_BARRIER();
    q->head = h + 1u;
    return 0;
}
 
static inline int spsc_pop(spsc_t *q, void *it)
{
    const uint32_t t = q->tail;
    if (q->head == t) return 0;                           
    SPSC_BARRIER();
    memcpy(it, &q->buf[(t & q->mask) * q->item], q->item);
    SPSC_BARRIER();
    q->tail = t + 1u;
    return 1;
}
 
static inline uint32_t spsc_count(const spsc_t *q) { return q->head - q->tail; }
 
#endif /* SPSC_H */