show of Float and Double closer to what ghc does

Author: atzedijkstra

EHC/src/rts/bc/prim.cc

@@ -426,7 +426,7 @@ PRIM GB_NodePtr primShowFloat( Float w )
 {
 	char buf[sizeof(Float)*10] ;
 	char *s = buf ;
-	sprintf( s, "%f", w ) ;
+	sprintf( s, "%-1.8g", w ) ;
 
 	GB_NodePtr n ;
 	int sz = strlen(buf) + 1 ; // ??? why +1
@@ -440,7 +440,7 @@ PRIM GB_NodePtr primShowDouble( Double w )
 {
 	char buf[sizeof(Double)*10] ;
 	char *s = buf ;
-	sprintf( s, "%lf", w ) ;
+	sprintf( s, "%-1.16g", w ) ;
 
 	GB_NodePtr n ;
 	int sz = strlen(buf) + 1 ; // ??? why +1

EHC/test/regress/99/FloatPrint1.hs

@@ -0,0 +1,39 @@
+{- ----------------------------------------------------------------------------------------
+   what    : Floating functions, on Float
+   expected: print with as much precision as possible (used to be 5 after comma)
+---------------------------------------------------------------------------------------- -}
+
+{-
+
+With GHC (8.0.1): 1.4142135623730951
+with UHC: 1.414214
+
+Is there any reason for the difference?
+
+Blocking agda/agda#1856.
+
+-}
+
+module Main where
+
+main = do
+  print $ sqrt (2.0 :: Float)
+  print $ sqrt (2.0 :: Double)
+  print $ sqrt (20000000.0 :: Float)
+  print $ sqrt (20000000.0 :: Double)
+  print $ sqrt (0.00000002 :: Float)
+  print $ sqrt (0.00000002 :: Double)
+  print $ sqrt (20000000000000000000.0 :: Float)
+  print $ sqrt (20000000000000000000.0 :: Double)
+  print $ sqrt (0.00000000000000000002 :: Float)
+  print $ sqrt (0.00000000000000000002 :: Double)
+  print $      (2.0 :: Float)
+  print $      (2.0 :: Double)
+  print $      (20000000.0 :: Float)
+  print $      (20000000.0 :: Double)
+  print $      (0.00000002 :: Float)
+  print $      (0.00000002 :: Double)
+  print $      (20000000000000000000.0 :: Float)
+  print $      (20000000000000000000.0 :: Double)
+  print $      (0.00000000000000000002 :: Float)
+  print $      (0.00000000000000000002 :: Double)