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tofu: Compare squares instead of square roots.

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* g10/Makefile.am (tofu_source) [USE_TOFU]: Remove sqrtu32.h and
sqrtu32.c.
* g10/sqrtu32.h, g10/sqrtu32.c: Removed files.
* g10/tofu.c: Compare squares instead of square roots.
--
The original code is a factor 11.5 slower than using libm's sqrt(),
which in turn is a factor 3.5 slower than using one multiplication
on the other side of the comparison.  Also, it's much simpler now.

Signed-off-by: Marcus Brinkmann <mb@g10code.com>
This commit is contained in:
Marcus Brinkmann 2017-07-06 13:52:24 +02:00
parent 1455b406e6
commit d245949766
4 changed files with 9 additions and 269 deletions
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18
g10/tofu.c
View file

@ -42,7 +42,6 @@
#include "../common/mkdir_p.h"
#include "gpgsql.h"
#include "../common/status.h"
#include "sqrtu32.h"
#include "tofu.h"
@ -2922,19 +2921,18 @@ write_stats_status (estream_t fp,
{
int summary;
int validity;
unsigned long days;
unsigned long days_sq;
/* Use the euclidean distance (m = sqrt(a^2 + b^2)) rather then the
sum of the magnitudes (m = a + b) to ensure a balance between
verified signatures and encrypted messages. */
days = sqrtu32 (signature_days * signature_days
+ encryption_days * encryption_days);
days_sq = signature_days * signature_days + encryption_days * encryption_days;
if (days < 1)
if (days_sq < 1)
validity = 1; /* Key without history. */
else if (days < 2 * BASIC_TRUST_THRESHOLD)
else if (days_sq < (2 * BASIC_TRUST_THRESHOLD) * (2 * BASIC_TRUST_THRESHOLD))
validity = 2; /* Key with too little history. */
else if (days < 2 * FULL_TRUST_THRESHOLD)
else if (days_sq < (2 * FULL_TRUST_THRESHOLD) * (2 * FULL_TRUST_THRESHOLD))
validity = 3; /* Key with enough history for basic trust. */
else
validity = 4; /* Key with a lot of history. */
@ -3232,9 +3230,9 @@ show_statistics (tofu_dbs_t dbs,
" one message to this key!\n"));
/* Cf. write_stats_status */
if (sqrtu32 (encryption_count * encryption_count
+ signature_count * signature_count)
< 2 * BASIC_TRUST_THRESHOLD)
if ((encryption_count * encryption_count
+ signature_count * signature_count)
< ((2 * BASIC_TRUST_THRESHOLD) * (2 * BASIC_TRUST_THRESHOLD)))
show_warning = 1;
}
}