1 files changed, 153 insertions, 0 deletions
diff --git a/misc/tlininterp.c b/misc/tlininterp.c
new file mode 100644
index 0000000..7db6791
--- /dev/null
+++ b/misc/tlininterp.c
@@ -0,0 +1,153 @@
+/*
+   tlininterp.c
+   David Rowe
+   Jan 2017
+
+   Fast linear interpolator for high oversampling rates.  Upsample
+   with a decent filter first such that the signal is "low pass" wrt
+   to the input sample rate.
+
+   build: gcc tlininterp.c -o tlininterp -Wall -O2
+
+*/
+
+#include <assert.h>
+#include <getopt.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+
+#define NBUF         1000
+#define SIGNED_16BIT    0
+#define SIGNED_8BIT     1
+
+void display_help(void) {
+    fprintf(stderr, "\nusage: tlininterp inputRawFile OutputRawFile OverSampleRatio [-c]\n");
+    fprintf(stderr, "\nUse - for stdin/stdout\n\n");
+    fprintf(stderr, "-c complex signed 16 bit input and output\n");
+    fprintf(stderr, "-d complex signed 16 bit input, complex signed 8 bit output\n");
+    fprintf(stderr, "-f +Fs/4 freq shift\n\n");
+}
+
+int main(int argc, char *argv[]) {
+    FILE       *fin, *fout;
+    short       left[2], right[2], out[2*NBUF], i;
+    float       oversample, t;
+    int8_t      out_s8[2*NBUF];
+    int         lo_i[3], lo_q[3];
+
+    if (argc < 3) {
+	display_help();
+	exit(1);
+    }
+
+    if (strcmp(argv[1], "-") == 0) 
+        fin = stdin;
+    else
+        fin = fopen(argv[1], "rb");
+    assert(fin != NULL);
+
+    if (strcmp(argv[2], "-") == 0) 
+        fout = stdout;
+    else
+        fout = fopen(argv[2], "wb");
+    assert(fout != NULL);
+
+    oversample = atof(argv[3]);
+    if (oversample <= 1) {
+ 	display_help();
+	exit(1);
+    }
+       
+    int channels = 1;
+    int freq_shift = 0;
+    lo_i[0] = -1; lo_i[1] =  0;
+    lo_q[0] =  0; lo_q[1] = -1;
+    int format = SIGNED_16BIT;
+    int opt;
+    while ((opt = getopt(argc, argv, "cdf")) != -1) {
+        switch (opt) {
+        case 'c': channels = 2; break;
+        case 'd': channels = 2; format = SIGNED_8BIT; break;
+        case 'f': freq_shift = 1; break;
+        default:
+            display_help();
+            exit(1);
+        }
+    }
+
+    for (i=0; i<channels; i++)
+        left[i] = 0;
+    t = 0.0;
+    int j = 0;
+    while(fread(&right, sizeof(short)*channels, 1, fin) == 1) {
+        while (t < 1.0) {
+
+            for (i=0; i<channels; i++) {
+                out[2*j+i] = (1.0 - t)*left[i] + t*right[i];
+            }
+
+            if (freq_shift) {
+
+                /* update local osc recursion */
+
+                lo_i[2] = -lo_i[0]; lo_q[2] = -lo_q[0];
+                
+                /* complex mixer to up-shift complex samples */
+
+                int a = out[2*j];
+                int b = out[2*j+1];
+                int c = lo_i[2];
+                int d = lo_q[2];
+
+                out[2*j]   = a*c - b*d;
+                out[2*j+1] = b*c + a*d;
+
+                //fprintf(stderr, "% d % d % 5d % 5d\n", lo_i[2], lo_q[2], out[0], out[1]);
+
+                /* update LO memory */
+
+                lo_i[0] = lo_i[1]; lo_i[1] = lo_i[2]; 
+                lo_q[0] = lo_q[1]; lo_q[1] = lo_q[2]; 
+            }
+
+            /* once we have enough samples write to disk */
+
+            j++;
+            if (j == NBUF) {
+                if (format == SIGNED_16BIT) {
+                    fwrite(&out, sizeof(short)*channels, NBUF, fout);
+                } else {
+                    for (i=0; i<channels*NBUF; i++) {
+                        out_s8[i] = out[i] >> 8;
+                    }
+                    fwrite(&out_s8, sizeof(int8_t)*channels, NBUF, fout);
+                }
+                j = 0;
+            }
+
+            t += 1.0/oversample;
+        }
+        
+        t -= 1.0;
+        for (i=0; i<channels; i++)
+            left[i] = right[i];
+    }
+
+    /* write remaining samples to disk */
+
+    if (format == SIGNED_16BIT) {
+        fwrite(&out, sizeof(short), j, fout);
+    } else {
+        for (i=0; i<j; i++) {
+            out_s8[i] = out[i] >> 8;
+        }
+        fwrite(&out_s8, sizeof(int8_t)*channels, j, fout);
+    }
+
+    fclose(fout);
+    fclose(fin);
+
+    return 0;
+}