[project @ 2001-08-29 14:32:49 by simonmar]

Fix *two* bugs in formatRealFloat:

The first one is in the Haskell 98 errata, namely that negative
exponents cause an infinite loop in the FFFixed case when no precision
is specified.  eg. `Numeric.showFFloat Nothing 0.02 ""'  I've modified
the code in the errata to properly handle the e == 0 case and to be
slightly more efficient when e > 0.

The second bug is this:

   Prelude> Numeric.showFFloat (Just 0) 0.02 ""
   "0."

diff --git a/ghc/lib/std/PrelFloat.lhs b/ghc/lib/std/PrelFloat.lhs
index 67eb2a7..ef065a4 100644 (file)
--- a/ghc/lib/std/PrelFloat.lhs
+++ b/ghc/lib/std/PrelFloat.lhs
@@ -1,5 +1,5 @@
 % ------------------------------------------------------------------------------
-% $Id: PrelFloat.lhs,v 1.11 2001/02/28 00:01:03 qrczak Exp $
+% $Id: PrelFloat.lhs,v 1.12 2001/08/29 14:32:49 simonmar Exp $
 %
 % (c) The University of Glasgow, 1994-2000
 %
@@ -496,13 +496,15 @@ formatRealFloat fmt decs x
        mk0 ls = case ls of { "" -> "0" ; _ -> ls}
       in
       case decs of
-       Nothing ->
-         let
-         f 0 s    rs  = mk0 (reverse s) ++ '.':mk0 rs
-         f n s    ""  = f (n-1) ('0':s) ""
-         f n s (r:rs) = f (n-1) (r:s) rs
-        in
-        f e "" ds
+       Nothing
+         | e <= 0    -> "0." ++ replicate (-e) '0' ++ ds
+         | otherwise ->
+            let
+               f 0 s    rs  = mk0 (reverse s) ++ '.':mk0 rs
+               f n s    ""  = f (n-1) ('0':s) ""
+               f n s (r:rs) = f (n-1) (r:s) rs
+            in
+               f e "" ds
        Just dec ->
         let dec' = max dec 0 in
        if e >= 0 then
@@ -516,8 +518,8 @@ formatRealFloat fmt decs x
          (ei,is') = roundTo base dec' (replicate (-e) 0 ++ is)
          d:ds' = map intToDigit (if ei > 0 then is' else 0:is')
         in
-        d : '.' : ds'
-        
+        d : (if null ds' then "" else '.':ds')
+
 
 roundTo :: Int -> Int -> [Int] -> (Int,[Int])
 roundTo base d is =