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Util: More efficient use of random data

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zzz
2020-08-01 12:59:50 +00:00
parent 29d2051a34
commit f4ac8e02f6
1 changed files with 4 additions and 19 deletions
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23
core/java/src/net/i2p/util/FortunaRandomSource.java
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@ -98,23 +98,16 @@ public class FortunaRandomSource extends RandomSource implements EntropyHarveste
if (n<=0) if (n<=0)
throw new IllegalArgumentException("n must be positive"); throw new IllegalArgumentException("n must be positive");
//// boolean isPowerOfTwo = (n & (n - 1)) == 0;
// this shortcut from sun's docs neither works nor is necessary.
//
//if ((n & -n) == n) {
// // i.e., n is a power of 2
// return (int)((n * (long)nextBits(31)) >> 31);
//}
// get at least 4 extra bits if possible for better // get at least 4 extra bits if possible for better
// distribution after the % // distribution after the %
// No extra needed if power of two. // No extra needed if power of two.
int numBits; int numBits;
if (n > 0x100000) if (n > 0x1000000 || (n > 0x100000 && !isPowerOfTwo))
numBits = 31; numBits = 31;
else if (n > 0x1000) else if (n > 0x10000 || (n > 0x1000 && !isPowerOfTwo))
numBits = 24; numBits = 24;
else if (n > 0x10) else if (n > 0x100 || (n > 0x10 && !isPowerOfTwo))
numBits = 16; numBits = 16;
else else
numBits = 8; numBits = 8;
@ -123,14 +116,6 @@ public class FortunaRandomSource extends RandomSource implements EntropyHarveste
rv = nextBits(numBits); rv = nextBits(numBits);
} }
return rv % n; return rv % n;
//int bits, val;
//do {
// bits = nextBits(31);
// val = bits % n;
//} while(bits - val + (n-1) < 0);
//
//return val;
} }
/** /**