[igt-dev] [PATCH i-g-t] lib/igt_audio: make audio_signal_detect take const data

[Simon Ser <simon.ser@intel.com>]

audio_signal_detect uses gsl_fft_real_radix2_transform which mutates the data
array. This can be surprising when calling audio_signal_detect and then read
again the data (e.g. for another check).

Instead of mutating the array, make audio_signal_detect less error-prone by
taking a const parameter. Do an internal copy before calling the gsl function.

Signed-off-by: Simon Ser <simon.ser@intel.com>
---
 lib/igt_audio.c | 13 +++++++++++--
 lib/igt_audio.h |  2 +-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/lib/igt_audio.c b/lib/igt_audio.c
index fd8cf07c0de3..a1dda50a3c09 100644
--- a/lib/igt_audio.c
+++ b/lib/igt_audio.c
@@ -251,11 +251,14 @@ void audio_signal_fill(struct audio_signal *signal, int16_t *buffer,
  * Checks that frequencies specified in signal, and only those, are included
  * in the input data.
  *
- * sampling_rate is given in Hz. data_len is the number of elements in data.
+ * sampling_rate is given in Hz. samples_len is the number of elements in
+ * samples.
  */
 bool audio_signal_detect(struct audio_signal *signal, int sampling_rate,
-			 int channel, double *data, size_t data_len)
+			 int channel, const double *samples, size_t samples_len)
 {
+	double *data;
+	size_t data_len = samples_len;
 	size_t bin_power_len = data_len / 2 + 1;
 	double bin_power[bin_power_len];
 	bool detected[FREQS_MAX];
@@ -264,6 +267,10 @@ bool audio_signal_detect(struct audio_signal *signal, int sampling_rate,
 	size_t i, j;
 	bool above, success;

+	/* gsl will mutate the array in-place, so make a copy */
+	data = malloc(samples_len * sizeof(double));
+	memcpy(data, samples, samples_len * sizeof(double));
+
 	/* Allowed error in Hz due to FFT step */
 	freq_accuracy = sampling_rate / data_len;
 	igt_debug("Allowed freq. error: %d Hz\n", freq_accuracy);
@@ -372,6 +379,8 @@ bool audio_signal_detect(struct audio_signal *signal, int sampling_rate,
 		}
 	}

+	free(data);
+
 	return success;
 }

diff --git a/lib/igt_audio.h b/lib/igt_audio.h
index 466e772a75a4..d5ba1caaca63 100644
--- a/lib/igt_audio.h
+++ b/lib/igt_audio.h
@@ -43,7 +43,7 @@ void audio_signal_reset(struct audio_signal *signal);
 void audio_signal_fill(struct audio_signal *signal, int16_t *buffer,
 		       size_t buffer_len);
 bool audio_signal_detect(struct audio_signal *signal, int sampling_rate,
-			 int channel, double *data, size_t data_len);
+			 int channel, const double *samples, size_t samples_len);
 size_t audio_extract_channel_s32_le(double *dst, size_t dst_cap,
 				    int32_t *src, size_t src_len,
 				    int n_channels, int channel);
--
2.21.0

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