py/formatfloat: Fix case of float format where leading digit was "10".

dpgeorge · dpgeorge · commit 03b8bb7ec9f2 · 2016-03-29T22:03:13.000+01:00
When taking the logarithm of the float to determine the exponent, there
are some edge cases that finish the log loop too large.  Eg for an
input value of 1e32-epsilon, this is actually less than 1e32 from the
log-loop table and finishes as 10.0e31 when it should be 1.0e32.  It
is thus rendered as :e32 (: comes after 9 in ascii).

There was the same problem with numbers less than 1.
diff --git a/py/formatfloat.c b/py/formatfloat.c
@@ -198,7 +198,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
             if (e == 0) {
                 e_sign_char = '+';
             }
-        } else {
+        } else if (fp_isless1(f)) {
             e++; 
             f *= FPCONST(10.0);
         }
@@ -250,6 +250,12 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
             }
         }
 
+        // It can be that f was right on the edge of an entry in pos_pow needs to be reduced
+        if (f >= FPCONST(10.0)) {
+            e += 1;
+            f *= FPCONST(0.1);
+        }
+
         // If the user specified fixed format (fmt == 'f') and e makes the 
         // number too big to fit into the available buffer, then we'll
         // switch to the 'e' format.

Original file line number	Diff line number	Diff line change
`@@ -198,7 +198,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch`
`198`	`198`	`if (e == 0) {`
`199`	`199`	`e_sign_char = '+';`
`200`	`200`	`}`
`201`		`- } else {`
	`201`	`+ } else if (fp_isless1(f)) {`
`202`	`202`	`e++;`
`203`	`203`	`f *= FPCONST(10.0);`
`204`	`204`	`}`
`@@ -250,6 +250,12 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch`
`250`	`250`	`}`
`251`	`251`	`}`
`252`	`252`
	`253`	`+ // It can be that f was right on the edge of an entry in pos_pow needs to be reduced`
	`254`	`+ if (f >= FPCONST(10.0)) {`
	`255`	`+ e += 1;`
	`256`	`+ f *= FPCONST(0.1);`
	`257`	`+ }`
	`258`	`+`
`253`	`259`	`// If the user specified fixed format (fmt == 'f') and e makes the`
`254`	`260`	`// number too big to fit into the available buffer, then we'll`
`255`	`261`	`// switch to the 'e' format.`