brlib repo creation

todo/circ_buf.h

@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * See Documentation/core-api/circular-buffers.rst for more information.
+ */
+
+#ifndef _LINUX_CIRC_BUF_H
+#define _LINUX_CIRC_BUF_H 1
+
+#define CIRC_BUF(name, type, bits)               \
+    struct s##name {                             \
+        type buf[1 << (bits)];                   \
+        int head;                                \
+        int tail;                                \
+    };
+
+struct circ_buf {
+	char *buf;
+	int head;
+	int tail;
+};
+
+/* Return count in buffer.  */
+#define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
+
+/* Return space available, 0..size-1.  We always leave one free char
+   as a completely full buffer has head == tail, which is the same as
+   empty.  */
+#define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
+
+/* Return count up to the end of the buffer.  Carefully avoid
+   accessing head and tail more than once, so they can change
+   underneath us without returning inconsistent results.  */
+#define CIRC_CNT_TO_END(head,tail,size) \
+	({int end = (size) - (tail); \
+	  int n = ((head) + end) & ((size)-1); \
+	  n < end ? n : end;})
+
+/* Return space available up to the end of the buffer.  */
+#define CIRC_SPACE_TO_END(head,tail,size) \
+	({int end = (size) - 1 - (head); \
+	  int n = (end + (tail)) & ((size)-1); \
+	  n <= end ? n : end+1;})
+
+#endif /* _LINUX_CIRC_BUF_H  */