## Fixed format floating point conversion does not round to even

Conversion of floating point numbers to a fixed numbers of decimals should use round-to-even rather that rounding up when the number is right between two possible results.

E.g., printf "%.1f" 0.45 should produce "0.4" rather than "0.5".

The heart of the problem is in libraries/base/GHC/Float.lhs. The roundTo function should be replaced by this

```
roundTo :: Int -> Int -> [Int] -> (Int,[Int])
roundTo base d is =
case f d True is of
x@(0,_) -> x
(1,xs) -> (1, 1:xs)
_ -> error "roundTo: bad Value"
where
b2 = base `quot` 2
f n _ [] = (0, replicate n 0)
f 0 e (x:xs) | x == b2 && e && all (== 0) xs = (0, []) -- Round to even when at exactly half the base
| otherwise = (if x >= b2 then 1 else 0, [])
f n _ (i:xs)
| i' == base = (1,0:ds)
| otherwise = (0,i':ds)
where
(c,ds) = f (n-1) (even i) xs
i' = c + i
```

I also (as the original author of the code) note that the large parts of that module was taken verbatim from the hbc libraries without attribution. :)

## Trac metadata

Trac field | Value |
---|---|

Version | 7.4.1 |

Type | Bug |

TypeOfFailure | OtherFailure |

Priority | normal |

Resolution | Unresolved |

Component | libraries/base |

Test case | |

Differential revisions | |

BlockedBy | |

Related | |

Blocking | |

CC | |

Operating system | |

Architecture |

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