audio: add float sample endianness converters

Commit ed2a4a7941 ("audio: proper support for float samples in
mixeng") added support for float audio samples. As there were no
audio frontend devices with float support at that time, the code
was limited to native endian float samples.

When nobody was paying attention, an audio device that supports
floating point samples crept in with commit eb9ad377bb
("virtio-sound: handle control messages and streams").

Add code for the audio subsystem to convert float samples to the
correct endianness.

The type punning code was taken from the PipeWire project.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20250515054429.7385-7-vr_qemu@t-online.de>

diff --git a/audio/audio.c b/audio/audio.c
index 3f5baf0cc65601e6f0d76ec01034ed63829a3a59..b58ad744330f74d65403c4ed790dad4c2f4a606d 100644 (file)
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -1892,7 +1892,8 @@ CaptureVoiceOut *AUD_add_capture(
         cap->buf = g_malloc0_n(hw->mix_buf.size, hw->info.bytes_per_frame);
 
         if (hw->info.is_float) {
-            hw->clip = mixeng_clip_float[hw->info.nchannels == 2];
+            hw->clip = mixeng_clip_float[hw->info.nchannels == 2]
+                [hw->info.swap_endianness];
         } else {
             hw->clip = mixeng_clip
                 [hw->info.nchannels == 2]

diff --git a/audio/audio_template.h b/audio/audio_template.h
index 7ccfec01168c46a6969f25a1f559824ea054e9f0..c29d79c44392b3c68d17f905928c95f39e931913 100644 (file)
--- a/audio/audio_template.h
+++ b/audio/audio_template.h
@@ -174,9 +174,11 @@ static int glue (audio_pcm_sw_init_, TYPE) (
 
     if (sw->info.is_float) {
 #ifdef DAC
-        sw->conv = mixeng_conv_float[sw->info.nchannels == 2];
+        sw->conv = mixeng_conv_float[sw->info.nchannels == 2]
+            [sw->info.swap_endianness];
 #else
-        sw->clip = mixeng_clip_float[sw->info.nchannels == 2];
+        sw->clip = mixeng_clip_float[sw->info.nchannels == 2]
+            [sw->info.swap_endianness];
 #endif
     } else {
 #ifdef DAC
@@ -303,9 +305,11 @@ static HW *glue(audio_pcm_hw_add_new_, TYPE)(AudioState *s,
 
     if (hw->info.is_float) {
 #ifdef DAC
-        hw->clip = mixeng_clip_float[hw->info.nchannels == 2];
+        hw->clip = mixeng_clip_float[hw->info.nchannels == 2]
+            [hw->info.swap_endianness];
 #else
-        hw->conv = mixeng_conv_float[hw->info.nchannels == 2];
+        hw->conv = mixeng_conv_float[hw->info.nchannels == 2]
+            [hw->info.swap_endianness];
 #endif
     } else {
 #ifdef DAC

diff --git a/audio/mixeng.c b/audio/mixeng.c
index 13e1ff9b080b788b4a209c74971ba4b340b34dc8..703ee5448fac2e46c4f2ee415045c9d78c04e832 100644 (file)
--- a/audio/mixeng.c
+++ b/audio/mixeng.c
@@ -283,6 +283,11 @@ static const float float_scale_reciprocal = 1.f / ((int64_t)INT32_MAX + 1);
 #endif
 #endif
 
+#define F32_TO_F32S(v) \
+    bswap32((union { uint32_t i; float f; }){ .f = (v) }.i)
+#define F32S_TO_F32(v) \
+    ((union { uint32_t i; float f; }){ .i = bswap32(v) }.f)
+
 static void conv_natural_float_to_mono(struct st_sample *dst, const void *src,
                                        int samples)
 {
@@ -294,6 +299,17 @@ static void conv_natural_float_to_mono(struct st_sample *dst, const void *src,
     }
 }
 
+static void conv_swap_float_to_mono(struct st_sample *dst, const void *src,
+                                    int samples)
+{
+    const uint32_t *in_f32s = src;
+
+    while (samples--) {
+        dst->r = dst->l = CONV_NATURAL_FLOAT(F32S_TO_F32(*in_f32s++));
+        dst++;
+    }
+}
+
 static void conv_natural_float_to_stereo(struct st_sample *dst, const void *src,
                                          int samples)
 {
@@ -306,9 +322,27 @@ static void conv_natural_float_to_stereo(struct st_sample *dst, const void *src,
     }
 }
 
-t_sample *mixeng_conv_float[2] = {
-    conv_natural_float_to_mono,
-    conv_natural_float_to_stereo,
+static void conv_swap_float_to_stereo(struct st_sample *dst, const void *src,
+                                      int samples)
+{
+    const uint32_t *in_f32s = src;
+
+    while (samples--) {
+        dst->l = CONV_NATURAL_FLOAT(F32S_TO_F32(*in_f32s++));
+        dst->r = CONV_NATURAL_FLOAT(F32S_TO_F32(*in_f32s++));
+        dst++;
+    }
+}
+
+t_sample *mixeng_conv_float[2][2] = {
+    {
+        conv_natural_float_to_mono,
+        conv_swap_float_to_mono,
+    },
+    {
+        conv_natural_float_to_stereo,
+        conv_swap_float_to_stereo,
+    }
 };
 
 static void clip_natural_float_from_mono(void *dst, const struct st_sample *src,
@@ -322,6 +356,17 @@ static void clip_natural_float_from_mono(void *dst, const struct st_sample *src,
     }
 }
 
+static void clip_swap_float_from_mono(void *dst, const struct st_sample *src,
+                                      int samples)
+{
+    uint32_t *out_f32s = dst;
+
+    while (samples--) {
+        *out_f32s++ = F32_TO_F32S(CLIP_NATURAL_FLOAT(src->l + src->r));
+        src++;
+    }
+}
+
 static void clip_natural_float_from_stereo(
     void *dst, const struct st_sample *src, int samples)
 {
@@ -334,9 +379,27 @@ static void clip_natural_float_from_stereo(
     }
 }
 
-f_sample *mixeng_clip_float[2] = {
-    clip_natural_float_from_mono,
-    clip_natural_float_from_stereo,
+static void clip_swap_float_from_stereo(
+    void *dst, const struct st_sample *src, int samples)
+{
+    uint32_t *out_f32s = dst;
+
+    while (samples--) {
+        *out_f32s++ = F32_TO_F32S(CLIP_NATURAL_FLOAT(src->l));
+        *out_f32s++ = F32_TO_F32S(CLIP_NATURAL_FLOAT(src->r));
+        src++;
+    }
+}
+
+f_sample *mixeng_clip_float[2][2] = {
+    {
+        clip_natural_float_from_mono,
+        clip_swap_float_from_mono,
+    },
+    {
+        clip_natural_float_from_stereo,
+        clip_swap_float_from_stereo,
+    }
 };
 
 void audio_sample_to_uint64(const void *samples, int pos,

diff --git a/audio/mixeng.h b/audio/mixeng.h
index a5f56d2c268b1c3829f8bb96580255d63c65f4b5..ead93ac2f783a1577bbecbd694d8588e2eac838f 100644 (file)
--- a/audio/mixeng.h
+++ b/audio/mixeng.h
@@ -42,9 +42,9 @@ typedef void (f_sample) (void *dst, const struct st_sample *src, int samples);
 extern t_sample *mixeng_conv[2][2][2][3];
 extern f_sample *mixeng_clip[2][2][2][3];
 
-/* indices: [stereo] */
-extern t_sample *mixeng_conv_float[2];
-extern f_sample *mixeng_clip_float[2];
+/* indices: [stereo][swap endianness] */
+extern t_sample *mixeng_conv_float[2][2];
+extern f_sample *mixeng_clip_float[2][2];
 
 void *st_rate_start (int inrate, int outrate);
 void st_rate_flow(void *opaque, st_sample *ibuf, st_sample *obuf,