Well this patch should solve it.
I don't know how many samples are processed so:
First patch is for situation when N*N fits in s32.
Second one uses two divisions, but doesn't have any abnormal restrictions for N.
Personally I think that two divisions won't hurt. :)
----- FILE: cx88-dsp_64bit_math1.patch -----
cx88-dsp: fixing 64bit math on 32bit kernels
Note the limitation of N.
Personally I know nothing about possible size of samples array.
From: Miroslav Sustek <sustmid...@centrum.cz>
Signed-off-by: Miroslav Sustek <sustmid...@centrum.cz>
diff -r 8aa1d865373c linux/drivers/media/video/cx88/cx88-dsp.c
--- a/linux/drivers/media/video/cx88/cx88-dsp.c Wed Apr 01 20:25:00 2009 +0000
+++ b/linux/drivers/media/video/cx88/cx88-dsp.c Tue Apr 07 00:08:48 2009 +0200
@@ -100,13 +100,22 @@
s32 s_prev2 = 0;
s32 coeff = 2*int_cos(freq);
u32 i;
+
+ s64 tmp;
+ u32 remainder;
+
for (i = 0; i < N; i++) {
s32 s = x[i] + ((s64)coeff*s_prev/32768) - s_prev2;
s_prev2 = s_prev;
s_prev = s;
}
- return (u32)(((s64)s_prev2*s_prev2 + (s64)s_prev*s_prev -
- (s64)coeff*s_prev2*s_prev/32768)/N/N);
+
+ tmp = (s64)s_prev2*s_prev2 + (s64)s_prev*s_prev -
+ (s64)coeff*s_prev2*s_prev/32768;
+
+ /* XXX: N must be low enough so that N*N fits in s32.
+ * Else we need two divisions. */
+ return (u32) div_s64_rem(tmp, N*N, &remainder);
}
static u32 freq_magnitude(s16 x[], u32 N, u32 freq)
----- FILE: cx88-dsp_64bit_math2.patch -----
cx88-dsp: fixing 64bit math on 32bit kernels
From: Miroslav Sustek <sustmid...@centrum.cz>
Signed-off-by: Miroslav Sustek <sustmid...@centrum.cz>
diff -r 8aa1d865373c linux/drivers/media/video/cx88/cx88-dsp.c
--- a/linux/drivers/media/video/cx88/cx88-dsp.c Wed Apr 01 20:25:00 2009 +0000
+++ b/linux/drivers/media/video/cx88/cx88-dsp.c Tue Apr 07 00:26:10 2009 +0200
@@ -100,13 +100,22 @@
s32 s_prev2 = 0;
s32 coeff = 2*int_cos(freq);
u32 i;
+
+ s64 tmp;
+ u32 remainder;
+
for (i = 0; i < N; i++) {
s32 s = x[i] + ((s64)coeff*s_prev/32768) - s_prev2;
s_prev2 = s_prev;
s_prev = s;
}
- return (u32)(((s64)s_prev2*s_prev2 + (s64)s_prev*s_prev -
- (s64)coeff*s_prev2*s_prev/32768)/N/N);
+
+ tmp = (s64)s_prev2*s_prev2 + (s64)s_prev*s_prev -
+ (s64)coeff*s_prev2*s_prev/32768;
+
+ tmp = div_s64_rem(tmp, N, &remainder);
+
+ return (u32)div_s64_rem(tmp, N, &remainder);
}
static u32 freq_magnitude(s16 x[], u32 N, u32 freq)
--
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