[Python-checkins] cpython: 1) Simplify comment -- one has to read the complete proof (available in ACL2)

Wed Apr 18 19:28:51 CEST 2012

http://hg.python.org/cpython/rev/aa8a25c161a4
changeset: 76404:aa8a25c161a4
user: Stefan Krah <skrah at bytereef.org>
date: Wed Apr 18 19:27:32 2012 +0200
summary:
 1) Simplify comment -- one has to read the complete proof (available in ACL2)
 in order to understand the algorithm anyway.
2) v->exp == -v->digits may be assumed.
3) Fix comment (v always shares data with a).
files:
 Modules/_decimal/libmpdec/mpdecimal.c | 15 +++++++--------
 1 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/Modules/_decimal/libmpdec/mpdecimal.c b/Modules/_decimal/libmpdec/mpdecimal.c
--- a/Modules/_decimal/libmpdec/mpdecimal.c
+++ b/Modules/_decimal/libmpdec/mpdecimal.c
@@ -6691,10 +6691,7 @@
 return i-1;
 }
 
-/*
- * Initial approximation for the reciprocal. Result has MPD_RDIGITS-2
- * significant digits.
- */
+/* Initial approximation for the reciprocal. */
 static void
 _mpd_qreciprocal_approx(mpd_t *z, const mpd_t *v, uint32_t *status)
 {
@@ -6702,6 +6699,8 @@
 mpd_uint_t dummy, word;
 int n;
 
+ assert(v->exp == -v->digits);
+
 _mpd_get_msdigits(&dummy, &word, v, MPD_RDIGITS);
 n = mpd_word_digits(word);
 word *= mpd_pow10[MPD_RDIGITS-n];
@@ -6710,7 +6709,7 @@
 (void)_mpd_shortdiv(z->data, p10data, 2, word);
 
 mpd_clear_flags(z);
- z->exp = -(v->exp + v->digits) - (MPD_RDIGITS-2);
+ z->exp = -(MPD_RDIGITS-2);
 z->len = (z->data[1] == 0) ? 1 : 2;
 mpd_setdigits(z);
 }
@@ -6723,7 +6722,7 @@
 mpd_context_t varcontext, maxcontext;
 mpd_t *z = result; /* current approximation */
 mpd_t *v; /* a, normalized to a number between 0.1 and 1 */
- MPD_NEW_SHARED(vtmp, a); /* by default v will share data with a */
+ MPD_NEW_SHARED(vtmp, a); /* v shares data with a */
 MPD_NEW_STATIC(s,0,0,0,0); /* temporary variable */
 MPD_NEW_STATIC(t,0,0,0,0); /* temporary variable */
 MPD_NEW_CONST(two,0,0,1,1,1,2); /* const 2 */
@@ -6732,9 +6731,9 @@
 uint8_t sign = mpd_sign(a);
 int i;
 
+ assert(result != a);
+
 v = &vtmp;
- assert(result != a);
-
 mpd_clear_flags(v);
 adj = v->digits + v->exp;
 v->exp = -v->digits;
-- 
Repository URL: http://hg.python.org/cpython
