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emacs-27 0a3682a: * src/timefns.c: Add comments.
From: |
Paul Eggert |
Subject: |
emacs-27 0a3682a: * src/timefns.c: Add comments. |
Date: |
Sun, 8 Mar 2020 04:16:55 -0400 (EDT) |
branch: emacs-27
commit 0a3682a566d5563e3d57defe49359cee236e0274
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>
* src/timefns.c: Add comments.
---
src/timefns.c | 32 ++++++++++++++++++++++++--------
1 file changed, 24 insertions(+), 8 deletions(-)
diff --git a/src/timefns.c b/src/timefns.c
index a08d3b8..8e2bb21 100644
--- a/src/timefns.c
+++ b/src/timefns.c
@@ -491,11 +491,14 @@ timespec_mpz (struct timespec t)
static Lisp_Object
timespec_ticks (struct timespec t)
{
+ /* For speed, use intmax_t arithmetic if it will do. */
intmax_t accum;
if (FASTER_TIMEFNS
&& !INT_MULTIPLY_WRAPV (t.tv_sec, TIMESPEC_HZ, &accum)
&& !INT_ADD_WRAPV (t.tv_nsec, accum, &accum))
return make_int (accum);
+
+ /* Fall back on bignum arithmetic. */
timespec_mpz (t);
return make_integer_mpz ();
}
@@ -505,12 +508,17 @@ timespec_ticks (struct timespec t)
static Lisp_Object
lisp_time_hz_ticks (struct lisp_time t, Lisp_Object hz)
{
+ /* For speed, just return TICKS if T is (TICKS . HZ). */
if (FASTER_TIMEFNS && EQ (t.hz, hz))
return t.ticks;
+
+ /* Check HZ for validity. */
if (FIXNUMP (hz))
{
if (XFIXNUM (hz) <= 0)
invalid_hz (hz);
+
+ /* For speed, use intmax_t arithmetic if it will do. */
intmax_t ticks;
if (FASTER_TIMEFNS && FIXNUMP (t.ticks) && FIXNUMP (t.hz)
&& !INT_MULTIPLY_WRAPV (XFIXNUM (t.ticks), XFIXNUM (hz), &ticks))
@@ -520,6 +528,7 @@ lisp_time_hz_ticks (struct lisp_time t, Lisp_Object hz)
else if (! (BIGNUMP (hz) && 0 < mpz_sgn (*xbignum_val (hz))))
invalid_hz (hz);
+ /* Fall back on bignum arithmetic. */
mpz_mul (mpz[0],
*bignum_integer (&mpz[0], t.ticks),
*bignum_integer (&mpz[1], hz));
@@ -533,9 +542,13 @@ lisp_time_seconds (struct lisp_time t)
{
if (!FASTER_TIMEFNS)
return lisp_time_hz_ticks (t, make_fixnum (1));
+
+ /* For speed, use EMACS_INT arithmetic if it will do. */
if (FIXNUMP (t.ticks) && FIXNUMP (t.hz))
return make_fixnum (XFIXNUM (t.ticks) / XFIXNUM (t.hz)
- (XFIXNUM (t.ticks) % XFIXNUM (t.hz) < 0));
+
+ /* For speed, inline what lisp_time_hz_ticks would do. */
mpz_fdiv_q (mpz[0],
*bignum_integer (&mpz[0], t.ticks),
*bignum_integer (&mpz[1], t.hz));
@@ -1116,21 +1129,22 @@ time_arith (Lisp_Object a, Lisp_Object b, bool subtract)
(subtract ? mpz_submul : mpz_addmul) (*iticks, *fa, *nb);
/* Normalize iticks/ihz by dividing both numerator and
- denominator by ig = gcd (iticks, ihz). However, if that
- would cause the denominator to become less than hzmin,
- rescale the denominator upwards from its ordinary value by
- multiplying numerator and denominator so that the denominator
- becomes at least hzmin. This rescaling avoids returning a
- timestamp that is less precise than both a and b, or a
- timestamp that looks obsolete when that might be a problem. */
+ denominator by ig = gcd (iticks, ihz). For speed, though,
+ skip this division if ihz = 1. */
mpz_t *ig = &mpz[3];
mpz_gcd (*ig, *iticks, *ihz);
-
if (!FASTER_TIMEFNS || mpz_cmp_ui (*ig, 1) > 0)
{
mpz_divexact (*iticks, *iticks, *ig);
mpz_divexact (*ihz, *ihz, *ig);
+ /* However, if dividing the denominator by ig would cause the
+ denominator to become less than hzmin, rescale the denominator
+ upwards by multiplying the normalized numerator and denominator
+ so that the resulting denominator becomes at least hzmin.
+ This rescaling avoids returning a timestamp that is less precise
+ than both a and b, or a timestamp that looks obsolete when that
+ might be a problem. */
if (!FASTER_TIMEFNS || mpz_cmp (*ihz, *hzmin) < 0)
{
/* Rescale straightforwardly. Although this might not
@@ -1144,6 +1158,8 @@ time_arith (Lisp_Object a, Lisp_Object b, bool subtract)
mpz_mul (*ihz, *ihz, *rescale);
}
}
+
+ /* mpz[0] and iticks now correspond to the (HZ . TICKS) pair. */
hz = make_integer_mpz ();
mpz_swap (mpz[0], *iticks);
ticks = make_integer_mpz ();
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