diff options
Diffstat (limited to 'bcprov/src/main/java/org/bouncycastle/math/ec/WNafL2RMultiplier.java')
| -rw-r--r-- | bcprov/src/main/java/org/bouncycastle/math/ec/WNafL2RMultiplier.java | 17 |
1 files changed, 6 insertions, 11 deletions
diff --git a/bcprov/src/main/java/org/bouncycastle/math/ec/WNafL2RMultiplier.java b/bcprov/src/main/java/org/bouncycastle/math/ec/WNafL2RMultiplier.java index 59a9313..90b0847 100644 --- a/bcprov/src/main/java/org/bouncycastle/math/ec/WNafL2RMultiplier.java +++ b/bcprov/src/main/java/org/bouncycastle/math/ec/WNafL2RMultiplier.java @@ -31,7 +31,7 @@ public class WNafL2RMultiplier extends AbstractECMultiplier int i = wnaf.length; /* - * NOTE This code optimizes the first window using the precomputed points to substitute an + * NOTE: We try to optimize the first window using the precomputed points to substitute an * addition for 2 or more doublings. */ if (i > 1) @@ -42,19 +42,14 @@ public class WNafL2RMultiplier extends AbstractECMultiplier int n = Math.abs(digit); ECPoint[] table = digit < 0 ? preCompNeg : preComp; - /* - * NOTE: We use this optimization conservatively, since some coordinate systems have - * significantly cheaper doubling relative to addition. - * - * (n << 2) selects precomputed values in the lower half of the table - * (n << 3) selects precomputed values in the lower quarter of the table - */ - //if ((n << 2) < (1 << width)) - if ((n << 3) < (1 << width)) + // Optimization can only be used for values in the lower half of the table + if ((n << 2) < (1 << width)) { int highest = LongArray.bitLengths[n]; - int lowBits = n ^ (1 << (highest - 1)); + + // TODO Get addition/doubling cost ratio from curve and compare to 'scale' to see if worth substituting? int scale = width - highest; + int lowBits = n ^ (1 << (highest - 1)); int i1 = ((1 << (width - 1)) - 1); int i2 = (lowBits << scale) + 1; |