spectrogram: remove arbitrary limit on height of spectrogram

Sox had an arbitrary limit of 8193 on the vertical axis size
based on MAX_FFT_SIZE=4096 and had fixed-size arrays for its data.
This is both wasteful of memory for smaller FFTs and stops us producing
more detailed output for no obvious reason.

This patch removes the size limit on Y-axis-height by making array
allocation dynamic. In practice, you can't remove the limit as getopt
insists on minimum and maximum values for numeric arguments, so we
copy the similarly arbitrary limit of 200000 from MAX_X_SIZE.

diff --git a/src/spectrogram.c b/src/spectrogram.c
index afb0b0e..b38d212 100644
--- a/src/spectrogram.c
+++ b/src/spectrogram.c
@@ -36,10 +36,13 @@
   #include <io.h>
 #endif
 
-#define MAX_FFT_SIZE 4096
 #define is_p2(x) !(x & (x - 1))
 
+/* These are arbitrary as there is no upper limit, but
+ * sox's getopt() needs an upper limit for each option, so...
+ */
 #define MAX_X_SIZE 200000
+#define MAX_Y_SIZE 200000
 
 typedef enum {Window_Hann, Window_Hamming, Window_Bartlett, Window_Rectangular, Window_Kaiser, Window_Dolph} win_type_t;
 static lsx_enum_item const window_options[] = {
@@ -71,8 +74,11 @@ typedef struct {
   int        dft_size, step_size, block_steps, block_num, rows, cols, read;
   int        x_size, end, end_min, last_end;
   sox_bool   truncated;
-  double     buf[MAX_FFT_SIZE], dft_buf[MAX_FFT_SIZE], window[MAX_FFT_SIZE+1];
-  double     block_norm, max, magnitudes[(MAX_FFT_SIZE>>1) + 1];
+  double     * buf;		/* [dft_size] */
+  double     * dft_buf;		/* [dft_size] */
+  double     * window;		/* [dft_size + 1] */
+  double     block_norm, max;
+  double     * magnitudes;	/* [(dft_size / 2) + 1] */
   float      * dBfs;
 } priv_t;
 
@@ -114,9 +120,9 @@ static int getopts(sox_effect_t * effp, int argc, char **argv)
 
   while ((c = lsx_getopt(&optstate)) != -1) switch (c) {
     GETOPT_NUMERIC(optstate, 'x', x_size0       , 100, MAX_X_SIZE)
-    GETOPT_NUMERIC(optstate, 'X', pixels_per_sec,  1 , 5000)
-    GETOPT_NUMERIC(optstate, 'y', y_size        , 64 , 1200)
-    GETOPT_NUMERIC(optstate, 'Y', Y_size        , 130, MAX_FFT_SIZE / 2 + 2)
+    GETOPT_NUMERIC(optstate, 'X', pixels_per_sec,  1 , MAX_X_SIZE)
+    GETOPT_NUMERIC(optstate, 'y', y_size        , 64 , MAX_Y_SIZE)
+    GETOPT_NUMERIC(optstate, 'Y', Y_size        , 130, MAX_Y_SIZE)
     GETOPT_NUMERIC(optstate, 'z', dB_range      , 20 , 180)
     GETOPT_NUMERIC(optstate, 'Z', gain          ,-100, 100)
     GETOPT_NUMERIC(optstate, 'q', spectrum_points, 0 , p->spectrum_points)
@@ -172,7 +178,7 @@ static double make_window(priv_t * p, int end)
   double sum = 0, * w = end < 0? p->window : p->window + end;
   int i, n = 1 + p->dft_size - abs(end);
 
-  if (end) memset(p->window, 0, sizeof(p->window));
+  if (end) memset(p->window, 0, sizeof(*(p->window)) * p->dft_size);
   for (i = 0; i < n; ++i) w[i] = 1;
   switch (p->win_type) {
     case Window_Hann: lsx_apply_hann(w, n); break;
@@ -190,10 +196,10 @@ static double make_window(priv_t * p, int end)
   return sum;
 }
 
-static double * rdft_init(int n)
+static double * rdft_init(size_t n)
 {
   double * q = lsx_malloc(2 * (n / 2 + 1) * n * sizeof(*q)), * p = q;
-  int i, j;
+  size_t i, j;
   for (j = 0; j <= n / 2; ++j) for (i = 0; i < n; ++i)
     *p++ = cos(2 * M_PI * j * i / n), *p++ = sin(2 * M_PI * j * i / n);
   return q;
@@ -260,11 +266,18 @@ static int start(sox_effect_t * effp)
   if (p->y_size) {
     p->dft_size = 2 * (p->y_size - 1);
     if (!is_p2(p->dft_size) && !effp->flow)
-      p->shared = rdft_init(p->dft_size);
+      p->shared = rdft_init((size_t)(p->dft_size));
   } else {
    int y = max(32, (p->Y_size? p->Y_size : 550) / effp->in_signal.channels - 2);
    for (p->dft_size = 128; p->dft_size <= y; p->dft_size <<= 1);
   }
+
+  /* Now that dft_size is set, allocate variable-sized elements of priv_t */
+  p->buf	= lsx_calloc(p->dft_size, sizeof(*(p->buf)));
+  p->dft_buf	= lsx_calloc(p->dft_size, sizeof(*(p->dft_buf)));
+  p->window	= lsx_calloc(p->dft_size + 1, sizeof(*(p->window)));
+  p->magnitudes = lsx_calloc((p->dft_size / 2) + 1, sizeof(*(p->magnitudes)));
+
   if (is_p2(p->dft_size) && !effp->flow)
     lsx_safe_rdft(p->dft_size, 1, p->dft_buf);
   lsx_debug("duration=%g x_size=%i pixels_per_sec=%g dft_size=%i", duration, p->x_size, pixels_per_sec, p->dft_size);
@@ -651,6 +664,10 @@ error: png_destroy_write_struct(&png, &png_info);
   free(png_rows);
   free(pixels);
   free(p->dBfs);
+  free(p->buf);
+  free(p->dft_buf);
+  free(p->window);
+  free(p->magnitudes);
   return SOX_SUCCESS;
 }