fifo 简单实现

#define FIFO_SIZE_T size_t#define FIFO_MIN 0x4000typedef struct {   char * data;   size_t allocation;   /* Number of bytes allocated for data. */   size_t item_size;    /* Size of each item in data */   size_t begin;        /* Offset of the first byte to read. */   size_t end;          /* 1 + Offset of the last byte byte to read. */} fifo_t;static void fifo_clear(fifo_t * f){   f->end = f->begin = 0;}static void * fifo_reserve(fifo_t * f, FIFO_SIZE_T n){   n *= f->item_size;   if (f->begin == f->end)      fifo_clear(f);   while (1) {      if (f->end + n <= f->allocation) {         void *p = f->data + f->end;         f->end += n;         return p;      }      if (f->begin > FIFO_MIN) {         memmove(f->data, f->data + f->begin, f->end - f->begin);         f->end -= f->begin;         f->begin = 0;         continue;      }      f->allocation += n;      f->data = (char *)realloc(f->data, f->allocation);   }}static void * fifo_write(fifo_t * f, FIFO_SIZE_T n, void const * data){   void * s = fifo_reserve(f, n);   if (data)      memcpy(s, data, n * f->item_size);   return s;}static void * fifo_read(fifo_t * f, FIFO_SIZE_T n, void * data){   char * ret = f->data + f->begin;   n *= f->item_size;   if (n > (FIFO_SIZE_T)(f->end - f->begin))      return NULL;   if (data)      memcpy(data, ret, (size_t)n);   f->begin += n;   return ret;}static void fifo_delete(fifo_t * f){   free(f->data);}static void fifo_create(fifo_t * f, FIFO_SIZE_T item_size){   f->item_size = item_size;   f->allocation = FIFO_MIN;   f->data = (char *)malloc(f->allocation);   fifo_clear(f);}
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