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use continued fractions to approximate a fraction if its numerator or denominator is too large

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Originally committed as revision 2405 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer
2003-10-20 22:33:53 +00:00
parent 1c0dcc391a
commit 5ed9f2e5aa
1 changed files with 26 additions and 14 deletions
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38
libavcodec/utils.c
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@@ -684,7 +684,7 @@ char av_get_pict_type_char(int pict_type){
int av_reduce(int *dst_nom, int *dst_den, int64_t nom, int64_t den, int64_t max){ int av_reduce(int *dst_nom, int *dst_den, int64_t nom, int64_t den, int64_t max){
int exact=1, sign=0; int exact=1, sign=0;
int64_t gcd, larger; int64_t gcd;
assert(den != 0); assert(den != 0);
@@ -698,22 +698,34 @@ int av_reduce(int *dst_nom, int *dst_den, int64_t nom, int64_t den, int64_t max)
sign= 1; sign= 1;
} }
for(;;){ //note is executed 1 or 2 times gcd = ff_gcd(nom, den);
gcd = ff_gcd(nom, den); nom /= gcd;
nom /= gcd; den /= gcd;
den /= gcd;
larger= FFMAX(nom, den); if(nom > max || den > max){
AVRational a0={0,1}, a1={1,0};
exact=0;
if(larger > max){ for(;;){
int64_t div= (larger + max - 1) / max; int64_t x= nom / den;
nom = (nom + div/2)/div; int64_t a2n= x*a1.num + a0.num;
den = (den + div/2)/div; int64_t a2d= x*a1.den + a0.den;
exact=0;
}else if(a2n > max || a2d > max) break;
break;
nom %= den;
a0= a1;
a1= (AVRational){a2n, a2d};
if(nom==0) break;
x= nom; nom=den; den=x;
}
nom= a1.num;
den= a1.den;
} }
assert(ff_gcd(nom, den) == 1);
if(sign) nom= -nom; if(sign) nom= -nom;
*dst_nom = nom; *dst_nom = nom;