- **Python**
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- - **Re: Adding a positive number and a negative number**
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Re: Adding a positive number and a negative number> In twoâ€™s complement representation, can adding one positive and one negative give you overflow?
> No. |

Re: Adding a positive number and a negative numberScott David Daniels wrote:
> Grant Edwards wrote: >> On 2009-01-30, MRAB <google@mrabarnett.plus.com> wrote: >>>> In two's complement representation, can adding one positive >>>> and one negative give you overflow? >>> No. >> AFAIK, in Python adding integers never gives you overlow >> regardless of sign. > > Right, but he wants his homework answer. And Python doesn't use pure two's complement notation when it promotes regular integers to longs. regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ |

Re: Adding a positive number and a negative numberOn Jan 31, 4:10*am, Scott David Daniels <Scott.Dani...@Acm.Org> wrote:
> Grant Edwards wrote: > > On 2009-01-30, MRAB <goo...@mrabarnett.plus.com> wrote: > >>> In two's complement representation, can adding one positive > >>> and one negative give you overflow? > >> No. > > AFAIK, in Python adding integers never gives you overlow > > regardless of sign. > > Right, but he wants his homework answer. For extra brownie points, here's a simple proof of the more general proposition that adding a non-negative integer p and a non-positive integer n can't overflow whatever the representation. Let a be the most negative integer and b the most positive. So we're given a <= n <= 0 <= p <= b and need to show that a <= (p + n) <= b. max(p) is b, max(n) is 0, so max(p + n) is b. Similarly min(p + n) is a. Q.E.D. IEEE 754 floating point? I don't know. Go read the standard :-) |

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