1 #ifndef _LINUX_CIRC_BUF_H 2 #define _LINUX_CIRC_BUF_H 1 3 4 struct circ_buf { 5 char *buf; 6 int head; 7 int tail; 8 }; 9 10 /* Return count in buffer. */ 11 #define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1)) 12 13 /* Return space available, 0..size-1. We always leave one free char 14 as a completely full buffer has head == tail, which is the same as 15 empty. */ 16 #define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size)) 17 18 /* Return count up to the end of the buffer. Carefully avoid 19 accessing head and tail more than once, so they can change 20 underneath us without returning inconsistent results. */ 21 #define CIRC_CNT_TO_END(head,tail,size) \ 22 ({int end = (size) - (tail); \ 23 int n = ((head) + end) & ((size)-1); \ 24 n < end ? n : end;}) 25 26 /* Return space available up to the end of the buffer. */ 27 #define CIRC_SPACE_TO_END(head,tail,size) \ 28 ({int end = (size) - 1 - (head); \ 29 int n = (end + (tail)) & ((size)-1); \ 30 n <= end ? n : end+1;}) 31 32 #endif /* _LINUX_CIRC_BUF_H */ 33
