On Mon, 6 Apr 2009, Miroslav Šustek wrote:
> 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.
Both patches are fine, beacuse in the current implementation N is not
bigger than 576. Thanks for fixing this problem.
Regards,
Marton
>
> 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 <sustmidown@xxxxxxxxxx>
> Signed-off-by: Miroslav Sustek <sustmidown@xxxxxxxxxx>
>
> 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 <sustmidown@xxxxxxxxxx>
> Signed-off-by: Miroslav Sustek <sustmidown@xxxxxxxxxx>
>
> 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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