audio: replace open-coded buffer arithmetic

Replace open-coded buffer arithmetic with the new function
audio_ring_posb(). That's the position in backward direction
of a given point at a given distance.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Message-Id: <20220301191311.26695-1-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

audio/audio.c

@@ -574,19 +574,13 @@ static size_t audio_pcm_sw_get_rpos_in(SWVoiceIn *sw)
 {
     HWVoiceIn *hw = sw->hw;
     ssize_t live = hw->total_samples_captured - sw->total_hw_samples_acquired;
-    ssize_t rpos;
 
     if (audio_bug(__func__, live < 0 || live > hw->conv_buf->size)) {
         dolog("live=%zu hw->conv_buf->size=%zu\n", live, hw->conv_buf->size);
         return 0;
     }
 
-    rpos = hw->conv_buf->pos - live;
-    if (rpos >= 0) {
-        return rpos;
-    } else {
-        return hw->conv_buf->size + rpos;
-    }
+    return audio_ring_posb(hw->conv_buf->pos, live, hw->conv_buf->size);
 }
 
 static size_t audio_pcm_sw_read(SWVoiceIn *sw, void *buf, size_t size)
@@ -1394,12 +1388,10 @@ void audio_generic_run_buffer_in(HWVoiceIn *hw)
 
 void *audio_generic_get_buffer_in(HWVoiceIn *hw, size_t *size)
 {
-    ssize_t start = (ssize_t)hw->pos_emul - hw->pending_emul;
+    size_t start;
 
-    if (start < 0) {
-        start += hw->size_emul;
-    }
-    assert(start >= 0 && start < hw->size_emul);
+    start = audio_ring_posb(hw->pos_emul, hw->pending_emul, hw->size_emul);
+    assert(start < hw->size_emul);
 
     *size = MIN(*size, hw->pending_emul);
     *size = MIN(*size, hw->size_emul - start);
@@ -1415,13 +1407,10 @@ void audio_generic_put_buffer_in(HWVoiceIn *hw, void *buf, size_t size)
 void audio_generic_run_buffer_out(HWVoiceOut *hw)
 {
     while (hw->pending_emul) {
-        size_t write_len, written;
-        ssize_t start = ((ssize_t) hw->pos_emul) - hw->pending_emul;
+        size_t write_len, written, start;
 
-        if (start < 0) {
-            start += hw->size_emul;
-        }
-        assert(start >= 0 && start < hw->size_emul);
+        start = audio_ring_posb(hw->pos_emul, hw->pending_emul, hw->size_emul);
+        assert(start < hw->size_emul);
 
         write_len = MIN(hw->pending_emul, hw->size_emul - start);
 

audio/audio_int.h

@@ -266,6 +266,19 @@ static inline size_t audio_ring_dist(size_t dst, size_t src, size_t len)
     return (dst >= src) ? (dst - src) : (len - src + dst);
 }
 
+/**
+ * audio_ring_posb() - returns new position in ringbuffer in backward
+ * direction at given distance
+ *
+ * @pos: current position in ringbuffer
+ * @dist: distance in ringbuffer to walk in reverse direction
+ * @len: size of ringbuffer
+ */
+static inline size_t audio_ring_posb(size_t pos, size_t dist, size_t len)
+{
+    return pos >= dist ? pos - dist : len - dist + pos;
+}
+
 #define dolog(fmt, ...) AUD_log(AUDIO_CAP, fmt, ## __VA_ARGS__)
 
 #ifdef DEBUG

audio/coreaudio.c

@@ -333,12 +333,10 @@ static OSStatus audioDeviceIOProc(
 
     len = frameCount * hw->info.bytes_per_frame;
     while (len) {
-        size_t write_len;
-        ssize_t start = ((ssize_t) hw->pos_emul) - hw->pending_emul;
-        if (start < 0) {
-            start += hw->size_emul;
-        }
-        assert(start >= 0 && start < hw->size_emul);
+        size_t write_len, start;
+
+        start = audio_ring_posb(hw->pos_emul, hw->pending_emul, hw->size_emul);
+        assert(start < hw->size_emul);
 
         write_len = MIN(MIN(hw->pending_emul, len),
                         hw->size_emul - start);

audio/sdlaudio.c

@@ -224,12 +224,11 @@ static void sdl_callback_out(void *opaque, Uint8 *buf, int len)
         /* dolog("callback_out: len=%d avail=%zu\n", len, hw->pending_emul); */
 
         while (hw->pending_emul && len) {
-            size_t write_len;
-            ssize_t start = (ssize_t)hw->pos_emul - hw->pending_emul;
-            if (start < 0) {
-                start += hw->size_emul;
-            }
-            assert(start >= 0 && start < hw->size_emul);
+            size_t write_len, start;
+
+            start = audio_ring_posb(hw->pos_emul, hw->pending_emul,
+                                    hw->size_emul);
+            assert(start < hw->size_emul);
 
             write_len = MIN(MIN(hw->pending_emul, len),
                             hw->size_emul - start);