Micro-optimization

Author: kovidgoyal

kitty/history.c

@@ -326,8 +326,9 @@ static inline char_type
 pagerhist_remove_char(PagerHistoryBuf *ph, unsigned *count, uint8_t record[8]) {
     uint32_t codep, state = UTF8_ACCEPT;
     *count = 0;
-    while (ringbuf_bytes_used(ph->ringbuf)) {
-        ringbuf_memmove_from(&record[*count], ph->ringbuf, 1);
+    size_t num = ringbuf_bytes_used(ph->ringbuf);
+    while (num--) {
+        record[*count] = ringbuf_move_char(ph->ringbuf);
         decode_utf8(&state, &codep, record[*count]);
         *count += 1;
         if (state == UTF8_REJECT) { codep = 0; break; }

kitty/ringbuf.c

@@ -291,6 +291,18 @@ ringbuf_memmove_from(void *dst, ringbuf_t src, size_t count)
     return src->tail;
 }
 
+unsigned char
+ringbuf_move_char(ringbuf_t src) {
+    assert(!ringbuf_is_empty(src));
+    const uint8_t *bufend = ringbuf_end(src);
+    assert(bufend > src->tail);
+    uint8_t ans = *src->tail;
+    src->tail += 1;
+    if (src->tail == bufend)
+        src->tail = src->buf;
+    return ans;
+}
+
 size_t
 ringbuf_memcpy_from(void *dst, const ringbuf_t src, size_t count)
 {

kitty/ringbuf.h

@@ -189,6 +189,11 @@ ringbuf_read(int fd, ringbuf_t rb, size_t count);
 void *
 ringbuf_memmove_from(void *dst, ringbuf_t src, size_t count);
 
+/* ringbuf_memmove_from() optimized for a single character.
+ * Must only be called if the ringbuf is not empty */
+unsigned char
+ringbuf_move_char(ringbuf_t src);
+
 /*
  * Same as ringbuf_memmove_from() except that it does not change the ringbuffer
  * and returns the actual number of bytes copied, which is the minimum of ringbuf_bytes_used