Ticket #3304: 0001-Adjust-behaviour-of-gcd.patch

File 0001-Adjust-behaviour-of-gcd.patch, 1.9 KB (added by daniel.is.fischer, 2 years ago)

  • GHC/Real.lhs 

    From c902382e3645777bf92f98fd8b873c0591921e25 Mon Sep 17 00:00:00 2001
From: Daniel Fischer <daniel.is.fischer@googlemail.com>
Date: Tue, 17 May 2011 22:53:40 +0200
Subject: [PATCH] Adjust behaviour of gcd

Change behaviour of 'gcd 0 0' from raising an exception to
returning 0 to make it total and conform to mathematical practice.
---
 GHC/Real.lhs |   12 +++---------
 1 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/GHC/Real.lhs b/GHC/Real.lhs
index 17d0452..0b4d4d5 100644
    a b  
    520520                  in if even e then (nn :% dd) else (negate nn :% dd) 
    521521 
    522522------------------------------------------------------- 
    523 -- | @'gcd' x y@ is the greatest (positive) integer that divides both @x@ 
     523-- | @'gcd' x y@ is the greatest (nonnegative) integer that divides both @x@ 
    524524-- and @y@; for example @'gcd' (-3) 6@ = @3@, @'gcd' (-3) (-6)@ = @3@, 
    525 -- @'gcd' 0 4@ = @4@.  @'gcd' 0 0@ raises a runtime error. 
     525-- @'gcd' 0 4@ = @4@.  @'gcd' 0 0@ = @0@. 
    526526gcd             :: (Integral a) => a -> a -> a 
    527 gcd 0 0         =  error "Prelude.gcd: gcd 0 0 is undefined" 
    528527gcd x y         =  gcd' (abs x) (abs y) 
    529528                   where gcd' a 0  =  a 
    530529                         gcd' a b  =  gcd' b (a `rem` b) 
    … …  
    539538#ifdef OPTIMISE_INTEGER_GCD_LCM 
    540539{-# RULES 
    541540"gcd/Int->Int->Int"             gcd = gcdInt 
    542 "gcd/Integer->Integer->Integer" gcd = gcdInteger' 
     541"gcd/Integer->Integer->Integer" gcd = gcdInteger 
    543542"lcm/Integer->Integer->Integer" lcm = lcmInteger 
    544543 #-} 
    545544 
    546 gcdInteger' :: Integer -> Integer -> Integer 
    547 gcdInteger' 0 0 = error "GHC.Real.gcdInteger': gcd 0 0 is undefined" 
    548 gcdInteger' a b = gcdInteger a b 
    549  
    550545gcdInt :: Int -> Int -> Int 
    551 gcdInt 0 0 = error "GHC.Real.gcdInt: gcd 0 0 is undefined" 
    552546gcdInt a b = fromIntegral (gcdInteger (fromIntegral a) (fromIntegral b)) 
    553547#endif 
    554548