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Re: [PATCH, libstdc++, complex] complex multiplication algorithm improved
- From: Paolo Carlini <paolo dot carlini at oracle dot com>
- To: Wang Feng <wanng dot fenng at gmail dot com>
- Cc: libstdc++ at gcc dot gnu dot org, Gabriel Dos Reis <gdr at integrable-solutions dot net>
- Date: Wed, 15 Sep 2010 10:40:15 +0200
- Subject: Re: [PATCH, libstdc++, complex] complex multiplication algorithm improved
- References: <AANLkTikfU1+E9K8B8-6XxvxsCLdu01TcznOTURKaE0vF@mail.gmail.com> <AANLkTikN2zvMaUJL0KPfdfi8ab5iJbtBs5iDeRybnFPD@mail.gmail.com>
On 09/15/2010 10:24 AM, Wang Feng wrote:
> Hi,
> Complex number multiplication done with 4 multiplications, but
> this one only need 3:
>
> (a+ib)(c+id) = ac - bd + i( bc + ad ) -- 4 multiplies
> = ac - bd + i[ ( a + b )( c + d ) - ac
> - bd ] -- 3 multiplies
>
Makes sense to me. Gaby, can you have a look?
Paolo.