Re: Q: division vs multiplication

t.hulek@imperial.ac.uk (Mr Tomas Hulek) writes:


[Can one optimize floating division by powers of two into something like a
shift?]


>I would imagine that division by 2.0 could be done very efficiently, just like
>division by 10 in our decimal system. But is it really so?


        On at least one set of machines (the IBM System 370/390 series), division
        of a floating point number by 2 is significantly faster than multiplication
        because the hardware has a special instruction for it.


        Of course, in a C program, division by 2 will only be faster when the
        compiler detects the situation and generates code using the instruction.
        A well-written compiler might detect both situations above and generate
        identical code.


+---------------------------------+
| Michael Quinlan |
| mikeq@primenet.com |
| http://www.primenet.com/~mikeq/ |
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