From 1733d0ffd869a4746c90565e5ad2aae305e9a8bf Mon Sep 17 00:00:00 2001
From: Sam Hocevar <sam@hocevar.net>
Date: Fri, 28 Jul 2017 13:37:07 +0200
Subject: [PATCH] math: tweak the real number printing routine.
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By adding a bias we ensure that 1.999… will be displayed as 2.0 as long as we
do not ask for too many digits, and that rounding is reasonable for most values.
Note that our need for proper rounding is not as high as for IEEE floats since
we have an insane amount of digits at our disposal.

Also we now get rid of trailing zeroes when printing reals.
---
 src/math/real.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/math/real.cpp b/src/math/real.cpp
index 4bc92db5..392cd256 100644
--- a/src/math/real.cpp
+++ b/src/math/real.cpp
@@ -1468,9 +1468,16 @@ template<> void real::sprintf(char *str, int ndigits) const
 
     /* Normalise x so that mantissa is in [1..9.999] */
     /* FIXME: better use int64_t when the cast is implemented */
+    /* FIXME: does not work with R_MAX and probably R_MIN */
     int exponent = ceil(log10(x));
     x *= pow(R_10(), -(real)exponent);
 
+    if (ndigits < 1)
+        ndigits = 1;
+
+    /* Add a bias to simulate some naive rounding */
+    x += real(4.99f) * pow(R_10(), -(real)(ndigits + 1));
+
     if (x < R_1())
     {
         x *= R_10();
@@ -1488,6 +1495,10 @@ template<> void real::sprintf(char *str, int ndigits) const
         x *= R_10();
     }
 
+    /* Remove excess trailing zeroes */
+    while (str[-1] == '0' && str[-2] != '.')
+        --str;
+
     /* Print exponent information */
     if (exponent)
         str += std::sprintf(str, "e%c%i",