py/formatfloat: Fix case where floats could render with a ":" character.

dpgeorge · dpgeorge · commit 7b050fa76c6a · 2018-03-01T16:02:59.000+11:00
Prior to this patch, some architectures (eg unix x86) could render floats
with a ":" character in them, eg 1e+39 would come out as ":e+38" (":" is
just after "9" in ASCII so this is like 10e+38).  This patch fixes some of
these cases.
diff --git a/py/formatfloat.c b/py/formatfloat.c
@@ -258,7 +258,7 @@ 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)) {
+        if ((int)f >= 10) {
             e += 1;
             f *= FPCONST(0.1);
         }
diff --git a/tests/float/float_format.py b/tests/float/float_format.py
@@ -9,3 +9,7 @@
 # make sure rounding is done at the correct precision
 for prec in range(8):
     print(('%%.%df' % prec) % 6e-5)
+
+# check certain cases that had a digit value of 10 render as a ":" character
+print('%.2e' % float('9' * 51 + 'e-39'))
+print('%.2e' % float('9' * 40 + 'e-21'))

Original file line number	Diff line number	Diff line change
`@@ -258,7 +258,7 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch`
`258`	`258`	`}`
`259`	`259`
`260`	`260`	`// It can be that f was right on the edge of an entry in pos_pow needs to be reduced`
`261`		`- if (f >= FPCONST(10.0)) {`
	`261`	`+ if ((int)f >= 10) {`
`262`	`262`	`e += 1;`
`263`	`263`	`f *= FPCONST(0.1);`
`264`	`264`	`}`