Commit | Line | Data |
---|---|---|
90fddabf DH |
1 | /* |
2 | * See Documentation/circular-buffers.txt for more information. | |
3 | */ | |
4 | ||
1da177e4 LT |
5 | #ifndef _LINUX_CIRC_BUF_H |
6 | #define _LINUX_CIRC_BUF_H 1 | |
7 | ||
8 | struct circ_buf { | |
9 | char *buf; | |
10 | int head; | |
11 | int tail; | |
12 | }; | |
13 | ||
14 | /* Return count in buffer. */ | |
15 | #define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1)) | |
16 | ||
17 | /* Return space available, 0..size-1. We always leave one free char | |
18 | as a completely full buffer has head == tail, which is the same as | |
19 | empty. */ | |
20 | #define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size)) | |
21 | ||
22 | /* Return count up to the end of the buffer. Carefully avoid | |
23 | accessing head and tail more than once, so they can change | |
24 | underneath us without returning inconsistent results. */ | |
25 | #define CIRC_CNT_TO_END(head,tail,size) \ | |
26 | ({int end = (size) - (tail); \ | |
27 | int n = ((head) + end) & ((size)-1); \ | |
28 | n < end ? n : end;}) | |
29 | ||
30 | /* Return space available up to the end of the buffer. */ | |
31 | #define CIRC_SPACE_TO_END(head,tail,size) \ | |
32 | ({int end = (size) - 1 - (head); \ | |
33 | int n = (end + (tail)) & ((size)-1); \ | |
34 | n <= end ? n : end+1;}) | |
35 | ||
36 | #endif /* _LINUX_CIRC_BUF_H */ |