[goffice] Tests: fix bit rounding.

[Morten Welinder <mortenw src gnome org>]

commit 132dd34769e257522eba25bc90f34bd0da07204e
Author: Morten Welinder <terra gnome org>
Date:   Wed Mar 9 10:58:05 2016 -0500

    Tests: fix bit rounding.

 ChangeLog         |    5 +++++
 tests/constants.c |   18 ++++++++++--------
 2 files changed, 15 insertions(+), 8 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 0d6761c..f45226f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2016-03-09  Morten Welinder  <terra gnome org>
+
+       * tests/constants.c (print_bits): Fix bit pattern rounding past
+       the break.
+
 2016-03-05  Morten Welinder  <terra gnome org>
 
        * goffice/math/go-complex.c (go_complex_sqrt): Fix accuracy of
diff --git a/tests/constants.c b/tests/constants.c
index 3a4dc0f..70b5317 100644
--- a/tests/constants.c
+++ b/tests/constants.c
@@ -53,15 +53,13 @@ static GOQuad qln10;
 static void
 print_bits (GOQuad const *qc)
 {
-       GOQuad qx = *qc;
-       GOQuad qhalf;
+       GOQuad qx = *qc, qd;
        int e;
        double s;
        int b;
-       int N = 53 + 5;
+       int N = 53 + 7;
 
-       qhalf.h = 0.5;
-       qhalf.l = 0;
+       g_return_if_fail (go_finite (qx.h) && qx.h != 0);
 
        if (qx.h < 0) {
                g_printerr ("-");
@@ -69,17 +67,21 @@ print_bits (GOQuad const *qc)
                qx.l = -qx.l;
        }
 
+       // Scale mantissa to [0.5 ; 1.0[
        (void)frexp (go_quad_value (&qx), &e);
        s = ldexp (1.0, -e);
        qx.h *= s;
        qx.l *= s;
 
+       // Add to cause rounding when we truncate below
+       go_quad_init (&qd, ldexp (0.5, -N));
+       go_quad_add (&qx, &qx, &qd);
+
        for (b = 0; b < N; b++) {
                GOQuad d;
                qx.h *= 2;
                qx.l *= 2;
-               // For the last bit we compare against 1/2 to simulate rounding.
-               go_quad_sub (&d, &qx, (b == (N - 1) ? &qhalf : &go_quad_one));
+               go_quad_sub (&d, &qx, &go_quad_one);
                if (go_quad_value (&d) >= 0) {
                        qx = d;
                        g_printerr ("1");
@@ -164,7 +166,7 @@ main (int argc, char **argv)
        GOQuad qc;
 
        g_printerr ("Determine for certain constants, c, whether its representation\n");
-       g_printerr ("as a double is more accurate than its inverse's.\n\n");
+       g_printerr ("as a double is more accurate than its inverse's representation.\n\n");
 
        state = go_quad_start ();