famoser / elliptic / 16578839410

coverage: 96.985% (+1.4%) from 95.58%
16578839410

Pull #15

github

web-flow 
Merge 4e78e6e8a into d917b1701
Pull Request #15: Improve bernstein math

274 of 279 new or added lines in 32 files covered. (98.21%)

35 existing lines in 3 files now uncovered.

1383 of 1426 relevant lines covered (96.98%)

8.58 hits per line

Source File
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0.0
/src/Math/Calculator/MGXCalculator.php
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<?php
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namespace Famoser\Elliptic\Math\Calculator;










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use Famoser\Elliptic\Math\Calculator\Swapper\ScalarSwapper;










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/**










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 * implements https://datatracker.ietf.org/doc/html/rfc7748#section-5










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 */










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class MGXCalculator extends AbstractCalculator










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{










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    use ScalarSwapper;










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    public function mul(\GMP $u, \GMP $factor): \GMP




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    {










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        // normalize to the element bit length to always execute the double-add loop a constant number of times











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        $factorBits = gmp_strval($factor, 2);




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        $normalizedFactorBits = str_pad($factorBits, $this->field->getElementBitLength(), '0', STR_PAD_LEFT);




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        // precompute constants











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        $a24 = gmp_div(gmp_sub($this->curve->getA(), 2), 4);




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        $p2 = gmp_sub($this->curve->getP(), 2);




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        $x1 = $u;




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        $x2 = gmp_init(1);




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        $z2 = gmp_init(0);




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        $x3 = $u;




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        $z3 = gmp_init(1);




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        $swap = 0;




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        for ($i = 0; $i < $this->field->getElementBitLength(); $i++) {




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            $swap ^= (int)$normalizedFactorBits[$i];




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            $this->conditionalSwapScalar($x2, $x3, $swap, $this->field->getElementBitLength());




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            $this->conditionalSwapScalar($z2, $z3, $swap, $this->field->getElementBitLength());




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            $swap = (int)$normalizedFactorBits[$i];




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            $A = $this->field->add($x2, $z2);




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            $AA = $this->field->sq($A);




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            $B = $this->field->sub($x2, $z2);




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            $BB = $this->field->sq($B);




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            $E = $this->field->sub($AA, $BB);




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            $C = $this->field->add($x3, $z3);




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            $D = $this->field->sub($x3, $z3);




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            $DA = $this->field->mul($D, $A);




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            $CB = $this->field->mul($C, $B);




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            $x3 = $this->field->sq(gmp_add($DA, $CB));




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            $z3 = $this->field->mul($x1, $this->field->sq($this->field->sub($DA, $CB)));




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            $x2 = $this->field->mul($AA, $BB);




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            $z2 = $this->field->mul($E, $this->field->add($AA, $this->field->mul($a24, $E)));




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        }










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        $this->conditionalSwapScalar($x2, $x3, $swap, $this->field->getElementBitLength());




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        $this->conditionalSwapScalar($z2, $z3, $swap, $this->field->getElementBitLength());




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        return $this->field->mul($x2, gmp_powm($z2, $p2, $this->curve->getP()));




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    }










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}
























    

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