port more from osmocom-analog

cellular/src/samplerate.rs

@@ -0,0 +1,45 @@
+struct SampleRate {
+    factor: f64,
+    filter_cutoff: f64,
+    down: DownSampler,
+    up: UpSampler,
+}
+
+struct DownSampler {
+    lp: IIRFilter,
+    last_sample: Sample,
+    in_index: f64,
+}
+
+struct UpSampler {
+    lp: IIRFilter,
+    current_sample: Sample,
+    last_sample: Sample,
+    in_index: f64,
+}
+
+impl SampleRate {
+    pub fn init(&mut self, low_samplerate: f64, high_samplerate: f64, filter_cutoff: f64) -> Result<(), i32> {
+        // Implementation goes here
+
+        Ok(())
+        // or Err(error_code) if there's an error
+    }
+
+    pub fn downsample(&mut self, state: SampleRate, samples: Sample, input_num: i32) -> Result<(), i32> {
+        Ok(())
+    }
+
+    pub fn upsample_input_num(&mut self, state: SampleRate, output_num: i32) -> Result<(), i32> {
+        Ok(())
+    }
+
+    pub fn upsample_output_num(&mut self, state: SampleRate, input_num: i32) -> Result<(), i32> {
+        Ok(())
+    }
+
+    pub fn upsample(&mut self, state: SampleRate, input: Sample, input_num: i32, output: Sample, output_num: i32) {
+        
+    } 
+
+}