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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,74 @@ | ||
| // BarrettMu, a class for performing Barrett modular reduction computations in | ||
| // JavaScript. | ||
| // | ||
| // Requires BigInt.js. | ||
| // | ||
| // Copyright 2004-2005 David Shapiro. | ||
| // | ||
| // You may use, re-use, abuse, copy, and modify this code to your liking, but | ||
| // please keep this header. | ||
| // | ||
| // Thanks! | ||
| // | ||
| // Dave Shapiro | ||
| // dave@ohdave.com | ||
|
|
||
| function BarrettMu(m) | ||
| { | ||
| this.modulus = biCopy(m); | ||
| this.k = biHighIndex(this.modulus) + 1; | ||
| var b2k = new BigInt(); | ||
| b2k.digits[2 * this.k] = 1; // b2k = b^(2k) | ||
| this.mu = biDivide(b2k, this.modulus); | ||
| this.bkplus1 = new BigInt(); | ||
| this.bkplus1.digits[this.k + 1] = 1; // bkplus1 = b^(k+1) | ||
| this.modulo = BarrettMu_modulo; | ||
| this.multiplyMod = BarrettMu_multiplyMod; | ||
| this.powMod = BarrettMu_powMod; | ||
| } | ||
|
|
||
| function BarrettMu_modulo(x) | ||
| { | ||
| var q1 = biDivideByRadixPower(x, this.k - 1); | ||
| var q2 = biMultiply(q1, this.mu); | ||
| var q3 = biDivideByRadixPower(q2, this.k + 1); | ||
| var r1 = biModuloByRadixPower(x, this.k + 1); | ||
| var r2term = biMultiply(q3, this.modulus); | ||
| var r2 = biModuloByRadixPower(r2term, this.k + 1); | ||
| var r = biSubtract(r1, r2); | ||
| if (r.isNeg) { | ||
| r = biAdd(r, this.bkplus1); | ||
| } | ||
| var rgtem = biCompare(r, this.modulus) >= 0; | ||
| while (rgtem) { | ||
| r = biSubtract(r, this.modulus); | ||
| rgtem = biCompare(r, this.modulus) >= 0; | ||
| } | ||
| return r; | ||
| } | ||
|
|
||
| function BarrettMu_multiplyMod(x, y) | ||
| { | ||
| /* | ||
| x = this.modulo(x); | ||
| y = this.modulo(y); | ||
| */ | ||
| var xy = biMultiply(x, y); | ||
| return this.modulo(xy); | ||
| } | ||
|
|
||
| function BarrettMu_powMod(x, y) | ||
| { | ||
| var result = new BigInt(); | ||
| result.digits[0] = 1; | ||
| var a = x; | ||
| var k = y; | ||
| while (true) { | ||
| if ((k.digits[0] & 1) != 0) result = this.multiplyMod(result, a); | ||
| k = biShiftRight(k, 1); | ||
| if (k.digits[0] == 0 && biHighIndex(k) == 0) break; | ||
| a = this.multiplyMod(a, a); | ||
| } | ||
| return result; | ||
| } | ||
|
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