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minor speed change to fnv_tool.cal

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Also note that 2^19 bits does not have a FNV prime.
This commit is contained in:
Landon Curt Noll
2023-07-26 15:47:19 -07:00
parent 80e841eded
commit 94bf264088
1 changed files with 6 additions and 6 deletions
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12
cal/fnv_tool.cal
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@@ -66,7 +66,7 @@
* NOTE: For n that is a power of 2 and n > 1024, you will find that * NOTE: For n that is a power of 2 and n > 1024, you will find that
* that FNV primes become so rare that that one may not find a suitable * that FNV primes become so rare that that one may not find a suitable
* FNV prime. For n = 2048, 4096, 8192, 16384, 32768, 65536, 131072 * FNV prime. For n = 2048, 4096, 8192, 16384, 32768, 65536, 131072
* and 262144, there is NO suitable FNV prime. * 262144, and 524288, there is NO suitable FNV prime.
* *
* As for as hashing goes, large values of n, even if an * As for as hashing goes, large values of n, even if an
* FNV hash may be found, are unlikely to be truly useful. :-) * FNV hash may be found, are unlikely to be truly useful. :-)
@@ -174,7 +174,7 @@ define find_fnv_prime(bits)
if (popcnt(bits) == 1) { if (popcnt(bits) == 1) {
if (bits > 1024) { if (bits > 1024) {
print "# WARNING: FNV primes for powers of 2 > 1024 are extremely rare."; print "# WARNING: FNV primes for powers of 2 > 1024 are extremely rare.";
print "# WARNING: There are no FNV primes for 2048, 4096, 8192, 16384, 327678, 65536, 131072, nor 262144."; print "# WARNING: There are no FNV primes for 2048, 4096, 8192, 16384, 327678, 65536, 131072, 262144, nor 524288.";
} }
print "# NOTE: bits a power of 2 and bits >= 32: bits is suitable for a true FNV hash"; print "# NOTE: bits a power of 2 and bits >= 32: bits is suitable for a true FNV hash";
print "n =", bits; print "n =", bits;
@@ -208,17 +208,17 @@ define find_fnv_prime(bits)
} }
/* /*
* reject potential p value that is not prime * reject p if p mod (2^40 - 2^24 - 1) <= (2^24 + 2^8 + 2^7)
*/ */
p = p_minus_b + b; p = p_minus_b + b;
if (ptest(p) == 0) { if ((p % (2^40 - 2^24 - 1)) <= (2^24 + 2^8 + 2^7)) {
continue; continue;
} }
/* /*
* accept p if p mod (2^40 - 2^24 - 1) > (2^24 + 2^8 + 2^7) * accept potential p value that is prime
*/ */
if ((p % (2^40 - 2^24 - 1)) > (2^24 + 2^8 + 2^7)) { if (ptest(p) == 1) {
return p; return p;
} }
} }