py/formatfloat.c: Fix format of floating point numbers near 1.0.

In particular, numbers which are less than 1.0 but which
round up to 1.0.

This also makes those numbers which round up to 1.0 to
print with e+00 rather than e-00 for those formats which
print exponents.

Addresses issue #1178.

1 files changed, 8 insertions, 2 deletions

diff --git a/py/formatfloat.c b/py/formatfloat.c
index e73215a7a..64f013147 100644
--- a/py/formatfloat.c
+++ b/py/formatfloat.c
@@ -142,8 +142,14 @@ int mp_format_float(float f, char *buf, size_t buf_size, char fmt, int prec, cha
                 num.f *= *pos_pow;
             }
         }
+        char first_dig = '0';
+        char e_sign_char = '-';
         if (num.f < 1.0F && num.f >= 0.9999995F) {
             num.f = 1.0F;
+            first_dig = '1';
+            if (e == 0) {
+                e_sign_char = '+';
+            }
         } else {
             e++; 
             num.f *= 10.0F;
@@ -155,7 +161,7 @@ int mp_format_float(float f, char *buf, size_t buf_size, char fmt, int prec, cha
         if (fmt == 'f' || (fmt == 'g' && e <= 4)) {
             fmt = 'f';
             dec = -1;
-            *s++ = '0';
+            *s++ = first_dig;
 
             if (prec + e + 1 > buf_remaining) {
                 prec = buf_remaining - e - 1;
@@ -175,7 +181,7 @@ int mp_format_float(float f, char *buf, size_t buf_size, char fmt, int prec, cha
         } else {
             // For e & g formats, we'll be printing the exponent, so set the
             // sign.
-            e_sign = '-';
+            e_sign = e_sign_char;
             dec = 0;
 
             if (prec > (buf_remaining - 6)) {