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vu_meter: Use the fixedpoint lib (moving flog there)

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@14103 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Robert Keevil 2007-07-31 17:23:49 +00:00
parent aea433c3e3
commit 98e6073906
3 changed files with 42 additions and 78 deletions
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30
apps/plugins/lib/fixedpoint.c
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@ -202,3 +202,33 @@ long cos_int(int val)
}
return 0;
}
/**
* Fixed-point natural log
* taken from http://www.quinapalus.com/efunc.html
* "The code assumes integers are at least 32 bits long. The (positive)
* argument and the result of the function are both expressed as fixed-point
* values with 16 fractional bits, although intermediates are kept with 28
* bits of precision to avoid loss of accuracy during shifts."
*/
long flog(int x) {
long t,y;
y=0xa65af;
if(x<0x00008000) x<<=16, y-=0xb1721;
if(x<0x00800000) x<<= 8, y-=0x58b91;
if(x<0x08000000) x<<= 4, y-=0x2c5c8;
if(x<0x20000000) x<<= 2, y-=0x162e4;
if(x<0x40000000) x<<= 1, y-=0x0b172;
t=x+(x>>1); if((t&0x80000000)==0) x=t,y-=0x067cd;
t=x+(x>>2); if((t&0x80000000)==0) x=t,y-=0x03920;
t=x+(x>>3); if((t&0x80000000)==0) x=t,y-=0x01e27;
t=x+(x>>4); if((t&0x80000000)==0) x=t,y-=0x00f85;
t=x+(x>>5); if((t&0x80000000)==0) x=t,y-=0x007e1;
t=x+(x>>6); if((t&0x80000000)==0) x=t,y-=0x003f8;
t=x+(x>>7); if((t&0x80000000)==0) x=t,y-=0x001fe;
x=0x80000000-x;
y-=x>>15;
return y;
}