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FFT plugin: eliminate 64-bit math. This should result in faster and probably more accurate calculations.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@25790 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Delyan Kratunov 2010-05-02 20:30:44 +00:00
parent 7f9d30ba3e
commit af466f3cbf
3 changed files with 21 additions and 23 deletions
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1
apps/plugins/fft/SOURCES
View file

@ -1,4 +1,3 @@
kiss_fft.c
kiss_fftr.c
fft.c
math.c

35
apps/plugins/fft/fft.c
View file

@ -307,8 +307,8 @@ struct {
/************************* End of globals *************************/
/************************* Math functions *************************/
#define QLOG_MAX 286286
#define QLIN_MAX 1534588906
#define QLOG_MAX 0x00040000
#define QLIN_MAX 0x5B000000
#define QLN_10 float_q16(2.302585093)
#define LIN_MAX (QLIN_MAX >> 16)
@ -350,24 +350,31 @@ void apply_window_func(char mode)
/* Calculates the magnitudes from complex numbers and returns the maximum */
int32_t calc_magnitudes(bool logarithmic)
{
int64_t tmp;
/* A major assumption made when calculating the Q*MAX constants
* is that the maximum magnitude is 29 bits long. */
uint32_t tmp;
size_t i;
int32_t max = -2147483647;
/* Calculate the magnitude, discarding the phase.
* The sum of the squares can easily overflow the 15-bit (s15.16)
* requirement for fsqrt, so we scale the data down */
int32_t max = 0;
/* Calculate the magnitude, discarding the phase. */
for (i = 0; i < ARRAYSIZE_PLOT; ++i)
{
tmp = output[i].r * output[i].r + output[i].i * output[i].i;
tmp <<= 16;
tmp = fsqrt64(tmp, 16);
if (logarithmic)
tmp = get_log_value(tmp & 0x7FFFFFFF);
if (tmp > 0x7FFFFFFF) tmp >>= 1; /* if our assumptions are correct,
this should never happen. It's just
a safeguard. */
if (tmp > 0)
{
tmp = fp_sqrt(tmp, 0); /* linear scaling, nothing
bad should happen */
tmp <<= 16;
if (logarithmic)
tmp = get_log_value(tmp);/* the log function
expects s15.16 values */
}
plot[i] = tmp;
if (plot[i] > max)

8
apps/plugins/fft/math.h
View file

@ -17,12 +17,4 @@
#define float_q15(a) float_q(a, 15)
#define float_q16(a) float_q(a, 16)
/**
* Fixed point square root via Newton-Raphson.
* @param a square root argument.
* @param fracbits specifies number of fractional bits in argument.
* @return Square root of argument in same fixed point format as input.
*/
int64_t fsqrt64(int64_t a, unsigned int fracbits);
#endif