generate_coefs: separate type conversion and packing

This makes it easier to apply patches to the resulting binary before
writing it to a file.

docs/DSP/free_dsp_rom/generate_coefs.py

@@ -1,13 +1,16 @@
 from numpy import *
 from struct import pack
 
-def pack_coefs(c):
+def convert_coefs(c):
     cw = list(zip(c[   :128][::-1],
                   c[128:256][::-1],
                   c[256:384][::-1],
                   c[384:   ][::-1]))
     m = max(sum(x) for x in cw)
-    return b''.join(pack('>4h', *(int(round(n / m * 32767)) for n in x)) for x in cw)
+    return [int(round(n / m * 32767)) & 0xffff for x in cw for n in x]
+
+def pack_coefs(short_coefs):
+    return b''.join(pack('>H', c) for c in short_coefs)
 
 x = linspace(-2, 2, 512, endpoint=False)
 
@@ -18,8 +21,7 @@ coef_1 = [sinc(n * 0.5)  for n in x] * w1
 coef_2 = [sinc(n * 0.75) for n in x] * w2
 coef_3 = [sinc(n)        for n in x] * w1
 
+short_coefs = convert_coefs(coef_1) + convert_coefs(coef_2) + convert_coefs(coef_3) + [0] * 512
+
 with open('dsp_coef.bin', 'wb') as f:
-    f.write(pack_coefs(coef_1))
-    f.write(pack_coefs(coef_2))
-    f.write(pack_coefs(coef_3))
-    f.write(b'\0' * 1024)
+    f.write(pack_coefs(short_coefs))