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author | Michael Sevakis <jethead71@rockbox.org> | 2010-06-02 08:34:10 +0000 |
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committer | Michael Sevakis <jethead71@rockbox.org> | 2010-06-02 08:34:10 +0000 |
commit | 30e2f42c82c6c558497aceb5ab0bea24ffeffa3a (patch) | |
tree | efdd88db6d56a941f11ee2c7d3a687287ca267ec /apps/fixedpoint.c | |
parent | bbe6c5a5e20b95eff80881cee1277a0e259cbcd4 (diff) | |
download | rockbox-30e2f42c82c6c558497aceb5ab0bea24ffeffa3a.tar.gz rockbox-30e2f42c82c6c558497aceb5ab0bea24ffeffa3a.zip |
FFT Plugin: Revamp the main code to rid it of 64-bit math. Use 32-bit kiss_fft_scalar because 16-bit integers are generally a poor choice for computation on-target. Simplify display code to speed it up. Add logarithmic frequency display (need keymappings, guessed on some). On dual-core, perform FFT on COP. Add some support function to fixedpoint.c. ... and stuff.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26470 a1c6a512-1295-4272-9138-f99709370657
Diffstat (limited to 'apps/fixedpoint.c')
-rw-r--r-- | apps/fixedpoint.c | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/apps/fixedpoint.c b/apps/fixedpoint.c index f9903f301f..fb89a8d30f 100644 --- a/apps/fixedpoint.c +++ b/apps/fixedpoint.c @@ -171,6 +171,35 @@ long fp_sqrt(long x, unsigned int fracbits) return b; } + +/* Accurate int sqrt with only elementary operations. (the above + * routine fails badly without enough iterations, more iterations + * than this requires -- [give that one a FIXME]). + * Snagged from: + * http://www.devmaster.net/articles/fixed-point-optimizations/ */ +unsigned long isqrt(unsigned long x) +{ + /* Adding CLZ could optimize this further */ + unsigned long g = 0; + int bshift = 15; + unsigned long b = 1ul << bshift; + + do + { + unsigned long temp = (g + g + b) << bshift; + + if (x > temp) + { + g += b; + x -= temp; + } + + b >>= 1; + } + while (bshift--); + + return g; +} #endif /* PLUGIN or CODEC */ @@ -256,6 +285,44 @@ long fp16_log(int x) { y-=x>>15; return y; } + +/** + * Fixed-point exponential + * taken from http://www.quinapalus.com/efunc.html + * "The code assumes integers are at least 32 bits long. The (non-negative) + * argument and the result of the function are both expressed as fixed-point + * values with 16 fractional bits. Notice that after 11 steps of the + * algorithm the constants involved become such that the code is simply + * doing a multiplication: this is explained in the note below. + * The extension to negative arguments is left as an exercise." + */ +long fp16_exp(int x) +{ + int t,y; + + y=0x00010000; + t=x-0x58b91; if(t>=0) x=t,y<<=8; + t=x-0x2c5c8; if(t>=0) x=t,y<<=4; + t=x-0x162e4; if(t>=0) x=t,y<<=2; + t=x-0x0b172; if(t>=0) x=t,y<<=1; + t=x-0x067cd; if(t>=0) x=t,y+=y>>1; + t=x-0x03920; if(t>=0) x=t,y+=y>>2; + t=x-0x01e27; if(t>=0) x=t,y+=y>>3; + t=x-0x00f85; if(t>=0) x=t,y+=y>>4; + t=x-0x007e1; if(t>=0) x=t,y+=y>>5; + t=x-0x003f8; if(t>=0) x=t,y+=y>>6; + t=x-0x001fe; if(t>=0) x=t,y+=y>>7; + if(x&0x100) y+=y>>8; + if(x&0x080) y+=y>>9; + if(x&0x040) y+=y>>10; + if(x&0x020) y+=y>>11; + if(x&0x010) y+=y>>12; + if(x&0x008) y+=y>>13; + if(x&0x004) y+=y>>14; + if(x&0x002) y+=y>>15; + if(x&0x001) y+=y>>16; + return y; +} #endif /* PLUGIN */ |