From f78933265835f632fff2d638f4cc51bf554ecd81 Mon Sep 17 00:00:00 2001
From: zimmerma <zimmerma@280ebfd0-de03-0410-8827-d642c229c3f4>
Date: Wed, 13 Dec 2017 21:18:23 +0000
Subject: [src/sub1sp.c] fixed bug in mpfr_sub1sp2() [tests/tsub1sp.c] added
 non-regression test

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@11974 280ebfd0-de03-0410-8827-d642c229c3f4
---
 src/sub1sp.c    |  1 +
 tests/tsub1sp.c | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/sub1sp.c b/src/sub1sp.c
index a2fbd8898..bc776ee1b 100644
--- a/src/sub1sp.c
+++ b/src/sub1sp.c
@@ -608,6 +608,7 @@ mpfr_sub1sp2 (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode,
             {
               ap[1] = (a1 << 1) | (a0 >> (GMP_NUMB_BITS - 1));
               a0 = (a0 << 1) | (sb >> (GMP_NUMB_BITS - 1));
+              sb <<= 1;
               bx --;
             }
           else
diff --git a/tests/tsub1sp.c b/tests/tsub1sp.c
index bda7efe24..5e0342fea 100644
--- a/tests/tsub1sp.c
+++ b/tests/tsub1sp.c
@@ -218,6 +218,24 @@ compare_sub_sub1sp (void)
     }
 }
 
+static void
+bug20171213 (void)
+{
+  mpfr_t a, b, c;
+
+  mpfr_init2 (a, 127);
+  mpfr_init2 (b, 127);
+  mpfr_init2 (c, 127);
+  mpfr_set_str_binary (b, "0.1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000E1");
+  mpfr_set_str_binary (c, "0.1000011010111101100101100110101111111001011001010000110000000000000000000000000000000000000000000000000000000000000000000000000E-74");
+  mpfr_sub (a, b, c, MPFR_RNDN);
+  mpfr_set_str_binary (b, "0.1111111111111111111111111111111111111111111111111111111111111111111111111101111001010000100110100110010100000001101001101011110E0");
+  MPFR_ASSERTN(mpfr_equal_p (a, b));
+  mpfr_clear (a);
+  mpfr_clear (b);
+  mpfr_clear (c);
+}
+
 int
 main (void)
 {
@@ -228,6 +246,7 @@ main (void)
   compare_sub_sub1sp ();
   test20170208 ();
   bug20170109 ();
+  bug20171213 ();
   check_special ();
   for (p = MPFR_PREC_MIN ; p < 200 ; p++)
     {
-- 
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