comparison src/c-ringbuf/ringbuf.c @ 216:1f18f47e29eb

Add ring buffer implementation

+/*
+ * ringbuf.c - C ring buffer (FIFO) implementation.
+ *
+ * Written in 2011 by Drew Hess <[e-mail]>.
+ *
+ * To the extent possible under law, the author(s) have dedicated all
+ * copyright and related and neighboring rights to this software to
+ * the public domain worldwide. This software is distributed without
+ * any warranty.
+ *
+ * You should have received a copy of the CC0 Public Domain Dedication
+ * along with this software. If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ */
+
+#include "ringbuf.h"
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <unistd.h>
+#include <sys/param.h>
+#include <assert.h>
+
+/*
+ * The code is written for clarity, not cleverness or performance, and
+ * contains many assert()s to enforce invariant assumptions and catch
+ * bugs. Feel free to optimize the code and to remove asserts for use
+ * in your own projects, once you're comfortable that it functions as
+ * intended.
+ */
+
+struct ringbuf_t
+{
+    uint8_t *buf;
+    uint8_t *head, *tail;
+    size_t size;
+};
+
+ringbuf_t
+ringbuf_new(size_t capacity)
+{
+    ringbuf_t rb = malloc(sizeof(struct ringbuf_t));
+    if (rb) {
+
+        /* One byte is used for detecting the full condition. */
+        rb->size = capacity + 1;
+        rb->buf = malloc(rb->size);
+        if (rb->buf)
+            ringbuf_reset(rb);
+        else {
+            free(rb);
+            return 0;
+        }
+    }
+    return rb;
+}
+
+size_t
+ringbuf_buffer_size(const struct ringbuf_t *rb)
+{
+    return rb->size;
+}
+
+void
+ringbuf_reset(ringbuf_t rb)
+{
+    rb->head = rb->tail = rb->buf;
+}
+
+void
+ringbuf_free(ringbuf_t *rb)
+{
+    assert(rb && *rb);
+    free((*rb)->buf);
+    free(*rb);
+    *rb = 0;
+}
+
+size_t
+ringbuf_capacity(const struct ringbuf_t *rb)
+{
+    return ringbuf_buffer_size(rb) - 1;
+}
+
+/*
+ * Return a pointer to one-past-the-end of the ring buffer's
+ * contiguous buffer. You shouldn't normally need to use this function
+ * unless you're writing a new ringbuf_* function.
+ */
+static const uint8_t *
+ringbuf_end(const struct ringbuf_t *rb)
+{
+    return rb->buf + ringbuf_buffer_size(rb);
+}
+
+size_t
+ringbuf_bytes_free(const struct ringbuf_t *rb)
+{
+    if (rb->head >= rb->tail)
+        return ringbuf_capacity(rb) - (rb->head - rb->tail);
+    else
+        return rb->tail - rb->head - 1;
+}
+
+size_t
+ringbuf_bytes_used(const struct ringbuf_t *rb)
+{
+    return ringbuf_capacity(rb) - ringbuf_bytes_free(rb);
+}
+
+int
+ringbuf_is_full(const struct ringbuf_t *rb)
+{
+    return ringbuf_bytes_free(rb) == 0;
+}
+
+int
+ringbuf_is_empty(const struct ringbuf_t *rb)
+{
+    return ringbuf_bytes_free(rb) == ringbuf_capacity(rb);
+}
+
+const void *
+ringbuf_tail(const struct ringbuf_t *rb)
+{
+    return rb->tail;
+}
+
+const void *
+ringbuf_head(const struct ringbuf_t *rb)
+{
+    return rb->head;
+}
+
+/*
+ * Given a ring buffer rb and a pointer to a location within its
+ * contiguous buffer, return the a pointer to the next logical
+ * location in the ring buffer.
+ */
+static uint8_t *
+ringbuf_nextp(ringbuf_t rb, const uint8_t *p)
+{
+    /*
+     * The assert guarantees the expression (++p - rb->buf) is
+     * non-negative; therefore, the modulus operation is safe and
+     * portable.
+     */
+    assert((p >= rb->buf) && (p < ringbuf_end(rb)));
+    return rb->buf + ((++p - rb->buf) % ringbuf_buffer_size(rb));
+}
+
+size_t
+ringbuf_findchr(const struct ringbuf_t *rb, int c, size_t offset)
+{
+    const uint8_t *bufend = ringbuf_end(rb);
+    size_t bytes_used = ringbuf_bytes_used(rb);
+    if (offset >= bytes_used)
+        return bytes_used;
+
+    const uint8_t *start = rb->buf +
+        (((rb->tail - rb->buf) + offset) % ringbuf_buffer_size(rb));
+    assert(bufend > start);
+    size_t n = MIN(bufend - start, bytes_used - offset);
+    const uint8_t *found = memchr(start, c, n);
+    if (found)
+        return offset + (found - start);
+    else
+        return ringbuf_findchr(rb, c, offset + n);
+}
+
+size_t
+ringbuf_memset(ringbuf_t dst, int c, size_t len)
+{
+    const uint8_t *bufend = ringbuf_end(dst);
+    size_t nwritten = 0;
+    size_t count = MIN(len, ringbuf_buffer_size(dst));
+    int overflow = count > ringbuf_bytes_free(dst);
+
+    while (nwritten != count) {
+
+        /* don't copy beyond the end of the buffer */
+        assert(bufend > dst->head);
+        size_t n = MIN(bufend - dst->head, count - nwritten);
+        memset(dst->head, c, n);
+        dst->head += n;
+        nwritten += n;
+
+        /* wrap? */
+        if (dst->head == bufend)
+            dst->head = dst->buf;
+    }
+
+    if (overflow) {
+        dst->tail = ringbuf_nextp(dst, dst->head);
+        assert(ringbuf_is_full(dst));
+    }
+
+    return nwritten;
+}
+
+void *
+ringbuf_memcpy_into(ringbuf_t dst, const void *src, size_t count)
+{
+    const uint8_t *u8src = src;
+    const uint8_t *bufend = ringbuf_end(dst);
+    int overflow = count > ringbuf_bytes_free(dst);
+    size_t nread = 0;
+
+    while (nread != count) {
+        /* don't copy beyond the end of the buffer */
+        assert(bufend > dst->head);
+        size_t n = MIN(bufend - dst->head, count - nread);
+        memcpy(dst->head, u8src + nread, n);
+        dst->head += n;
+        nread += n;
+
+        /* wrap? */
+        if (dst->head == bufend)
+            dst->head = dst->buf;
+    }
+
+    if (overflow) {
+        dst->tail = ringbuf_nextp(dst, dst->head);
+        assert(ringbuf_is_full(dst));
+    }
+
+    return dst->head;
+}
+
+ssize_t
+ringbuf_read(int fd, ringbuf_t rb, size_t count)
+{
+    const uint8_t *bufend = ringbuf_end(rb);
+    size_t nfree = ringbuf_bytes_free(rb);
+
+    /* don't write beyond the end of the buffer */
+    assert(bufend > rb->head);
+    count = MIN(bufend - rb->head, count);
+    ssize_t n = read(fd, rb->head, count);
+    if (n > 0) {
+        assert(rb->head + n <= bufend);
+        rb->head += n;
+
+        /* wrap? */
+        if (rb->head == bufend)
+            rb->head = rb->buf;
+
+        /* fix up the tail pointer if an overflow occurred */
+        if (n > nfree) {
+            rb->tail = ringbuf_nextp(rb, rb->head);
+            assert(ringbuf_is_full(rb));
+        }
+    }
+
+    return n;
+}
+
+void *
+ringbuf_memcpy_from(void *dst, ringbuf_t src, size_t count, bool destroy)
+{
+    size_t bytes_used = ringbuf_bytes_used(src);
+    if (count > bytes_used)
+        return 0;
+
+    uint8_t *u8dst = dst;
+    const uint8_t *bufend = ringbuf_end(src);
+    uint8_t *tail = src->tail;
+    size_t nwritten = 0;
+    while (nwritten != count) {
+        assert(bufend > src->tail);
+        size_t n = MIN(bufend - src->tail, count - nwritten);
+        memcpy(u8dst + nwritten, src->tail, n);
+        src->tail += n;
+        nwritten += n;
+
+        /* wrap ? */
+        if (src->tail == bufend)
+            src->tail = src->buf;
+    }
+
+    if (!destroy)
+    {
+        src->tail = tail;
+    }
+    
+    assert(count + ringbuf_bytes_used(src) == bytes_used);
+    return src->tail;
+}
+
+ssize_t
+ringbuf_write(int fd, ringbuf_t rb, size_t count)
+{
+    size_t bytes_used = ringbuf_bytes_used(rb);
+    if (count > bytes_used)
+        return 0;
+
+    const uint8_t *bufend = ringbuf_end(rb);
+    assert(bufend > rb->head);
+    count = MIN(bufend - rb->tail, count);
+    ssize_t n = write(fd, rb->tail, count);
+    if (n > 0) {
+        assert(rb->tail + n <= bufend);
+        rb->tail += n;
+
+        /* wrap? */
+        if (rb->tail == bufend)
+            rb->tail = rb->buf;
+
+        assert(n + ringbuf_bytes_used(rb) == bytes_used);
+    }
+
+    return n;
+}
+
+void *
+ringbuf_copy(ringbuf_t dst, ringbuf_t src, size_t count)
+{
+    size_t src_bytes_used = ringbuf_bytes_used(src);
+    if (count > src_bytes_used)
+        return 0;
+    int overflow = count > ringbuf_bytes_free(dst);
+
+    const uint8_t *src_bufend = ringbuf_end(src);
+    const uint8_t *dst_bufend = ringbuf_end(dst);
+    size_t ncopied = 0;
+    while (ncopied != count) {
+        assert(src_bufend > src->tail);
+        size_t nsrc = MIN(src_bufend - src->tail, count - ncopied);
+        assert(dst_bufend > dst->head);
+        size_t n = MIN(dst_bufend - dst->head, nsrc);
+        memcpy(dst->head, src->tail, n);
+        src->tail += n;
+        dst->head += n;
+        ncopied += n;
+
+        /* wrap ? */
+        if (src->tail == src_bufend)
+            src->tail = src->buf;
+        if (dst->head == dst_bufend)
+            dst->head = dst->buf;
+    }
+
+    assert(count + ringbuf_bytes_used(src) == src_bytes_used);
+    
+    if (overflow) {
+        dst->tail = ringbuf_nextp(dst, dst->head);
+        assert(ringbuf_is_full(dst));
+    }
+
+    return dst->head;
+}