Speed up generation of Unicode hash functions.

j-naylor · j-naylor · commit ba958299eaf3 · 2021-08-12T09:08:56.000-04:00
Sets of Unicode keys are picky about the primes used when generating
a perfect hash function for them. Callers can spend many seconds
iterating through all the possible combinations of candidate
multipliers and seeds to find one that works.

Unicode updates typically happen only once a year, but it still makes
development and testing of Unicode scripts unnecessarily slow. To fix,
iterate over the primes in the innermost loop. This does not change
any existing functions checked into the tree.
diff --git a/src/tools/PerfectHash.pm b/src/tools/PerfectHash.pm
@@ -87,13 +87,13 @@ sub generate_hash_function
 	my $hash_seed2;
 	my @subresult;
   FIND_PARAMS:
-	foreach (17, 31, 127, 8191)
+	for ($hash_seed1 = 0; $hash_seed1 < 10; $hash_seed1++)
 	{
-		$hash_mult2 = $_;    # "foreach $hash_mult2" doesn't work
-		for ($hash_seed1 = 0; $hash_seed1 < 10; $hash_seed1++)
+		for ($hash_seed2 = 0; $hash_seed2 < 10; $hash_seed2++)
 		{
-			for ($hash_seed2 = 0; $hash_seed2 < 10; $hash_seed2++)
+			foreach (17, 31, 127, 8191)
 			{
+				$hash_mult2 = $_;    # "foreach $hash_mult2" doesn't work
 				@subresult = _construct_hash_table(
 					$keys_ref,   $hash_mult1, $hash_mult2,
 					$hash_seed1, $hash_seed2);

Original file line number	Diff line number	Diff line change
`@@ -87,13 +87,13 @@ sub generate_hash_function`
`87`	`87`	`my $hash_seed2;`
`88`	`88`	`my @subresult;`
`89`	`89`	`FIND_PARAMS:`
`90`		`- foreach (17, 31, 127, 8191)`
	`90`	`+ for ($hash_seed1 = 0; $hash_seed1 < 10; $hash_seed1++)`
`91`	`91`	`{`
`92`		`- $hash_mult2 = $_; # "foreach $hash_mult2" doesn't work`
`93`		`- for ($hash_seed1 = 0; $hash_seed1 < 10; $hash_seed1++)`
	`92`	`+ for ($hash_seed2 = 0; $hash_seed2 < 10; $hash_seed2++)`
`94`	`93`	`{`
`95`		`- for ($hash_seed2 = 0; $hash_seed2 < 10; $hash_seed2++)`
	`94`	`+ foreach (17, 31, 127, 8191)`
`96`	`95`	`{`
	`96`	`+ $hash_mult2 = $_; # "foreach $hash_mult2" doesn't work`
`97`	`97`	`@subresult = _construct_hash_table(`
`98`	`98`	`$keys_ref, $hash_mult1, $hash_mult2,`
`99`	`99`	`$hash_seed1, $hash_seed2);`