diff options
author | vlefevre <vlefevre@280ebfd0-de03-0410-8827-d642c229c3f4> | 2015-02-27 10:16:42 +0000 |
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committer | vlefevre <vlefevre@280ebfd0-de03-0410-8827-d642c229c3f4> | 2015-02-27 10:16:42 +0000 |
commit | ce590af8525020d476d4a3c000ddcfb975f8de78 (patch) | |
tree | 9518586f96591ae07b4312a9974ee5cf6fed3531 /src/sub1sp.c | |
parent | f3d957fbf2fd3e48ec18d33373b697e086ccfecb (diff) | |
download | mpfr-ce590af8525020d476d4a3c000ddcfb975f8de78.tar.gz |
[src/sub1sp.c] Avoid an unnecessary mpn_lshift after an mpn_sub_1 when
the initial value was a power of two.
git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@9328 280ebfd0-de03-0410-8827-d642c229c3f4
Diffstat (limited to 'src/sub1sp.c')
-rw-r--r-- | src/sub1sp.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/src/sub1sp.c b/src/sub1sp.c index 5e4703b9b..d8f6e7513 100644 --- a/src/sub1sp.c +++ b/src/sub1sp.c @@ -694,7 +694,9 @@ mpfr_sub1sp (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode) { /* ap was a power of 2, and we lose a bit */ /* Now it is 0111111111111111111[00000 */ - mpn_lshift(ap, ap, n, 1); + /* The following 2 lines are equivalent to: mpn_lshift(ap, ap, n, 1); */ + ap[0] <<= 1; + ap[n-1] |= MPFR_LIMB_HIGHBIT; bx--; /* And the lost bit x depends on Cp+1, and Cp */ /* Compute Cp+1 if it isn't already compute (ie d==1) */ @@ -742,10 +744,10 @@ mpfr_sub1sp (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode) if (MPFR_UNLIKELY(ap[n-1] == MPFR_LIMB_HIGHBIT)) { mp_size_t k = n-1; - do { + do k--; - } while (k>=0 && ap[k]==0); - if (MPFR_UNLIKELY(k<0)) + while (k >= 0 && ap[k] == 0); + if (MPFR_UNLIKELY (k < 0)) { /* It is a power of 2! */ /* Compute Cp+1 if it isn't already compute (ie d==1) */ @@ -763,11 +765,10 @@ mpfr_sub1sp (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode) { DEBUG( printf("(Truncate) Do sub\n") ); mpn_sub_1 (ap, ap, n, MPFR_LIMB_ONE << sh); - mpn_lshift(ap, ap, n, 1); - ap[0] |= MPFR_LIMB_ONE<<sh; + ap[n-1] |= MPFR_LIMB_HIGHBIT; bx--; /* FIXME: Explain why it works (or why not)... */ - inexact = (bcp1 == 0) ? 0 : (rnd_mode==MPFR_RNDN) ? -1 : 1; + inexact = (bcp1 == 0) ? 0 : (rnd_mode == MPFR_RNDN) ? -1 : 1; goto end_of_sub; } } |