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Change the token prehash function for better convergence

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Combining arithmetric (add) and bitwise (xor) mixing seems to give
better result than either.

With the new prehash function, we find a valid hash much quicker.
This commit is contained in:
H. Peter Anvin 2007-09-18 12:38:07 -07:00
parent 3ce3715fba
commit 5255fd1f36
3 changed files with 6 additions and 6 deletions
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4
perllib/phash.ph
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@ -42,8 +42,8 @@ sub prehash($$$) {
foreach $c (unpack("C*", $key)) {
$ko1 = $k1; $ko2 = $k2;
$k1 = int32(rot($ko1,$s0)-rot($ko2, $s1)+$c);
$k2 = int32(rot($ko2,$s2)-rot($ko1, $s3)+$c);
$k1 = int32(rot($ko1,$s0)^int32(rot($ko2, $s1)+$c));
$k2 = int32(rot($ko2,$s2)^int32(rot($ko1, $s3)+$c));
}
# Create a bipartite graph...

4
pptok.pl
View File

@ -191,8 +191,8 @@ if ($what eq 'c') {
print OUT " while ((c = *p++) != 0) {\n";
print OUT " uint32_t kn1, kn2;\n";
print OUT " c |= 0x20; /* convert to lower case */\n";
printf OUT " kn1 = rot(k1,%2d) - rot(k2,%2d) + c;\n", ${$sv}[0], ${$sv}[1];
printf OUT " kn2 = rot(k2,%2d) - rot(k1,%2d) + c;\n", ${$sv}[2], ${$sv}[3];
printf OUT " kn1 = rot(k1,%2d)^(rot(k2,%2d) + c);\n", ${$sv}[0], ${$sv}[1];
printf OUT " kn2 = rot(k2,%2d)^(rot(k1,%2d) + c);\n", ${$sv}[2], ${$sv}[3];
print OUT " k1 = kn1; k2 = kn2;\n";
print OUT " }\n";
print OUT "\n";

4
tokhash.pl
View File

@ -187,8 +187,8 @@ print " const char *p = token;\n";
print "\n";
print " while ((c = *p++) != 0) {\n";
printf " uint32_t kn1 = rot(k1,%2d) - rot(k2,%2d) + c;\n", ${$sv}[0], ${$sv}[1];
printf " uint32_t kn2 = rot(k2,%2d) - rot(k1,%2d) + c;\n", ${$sv}[2], ${$sv}[3];
printf " uint32_t kn1 = rot(k1,%2d)^(rot(k2,%2d) + c);\n", ${$sv}[0], ${$sv}[1];
printf " uint32_t kn2 = rot(k2,%2d)^(rot(k1,%2d) + c);\n", ${$sv}[2], ${$sv}[3];
print " k1 = kn1; k2 = kn2;\n";
print " }\n";
print "\n";