Re: "Shifting" floating point numbers



Jordan Abel wrote On 03/21/06 15:51,:
On 2006-03-21, woessner@xxxxxxxxx <woessner@xxxxxxxxx> wrote:

Does anyone know of a fast way to multiply floating point numbers by
powers of two? Conceptually, all you need to do is add to the
mantissa. But can I write C code (or x86 assembly) to accomplish this
without a full-blown multiply?

For example, I'd like to be able to do the following very quickly:

double x;
double y;

x = 42.13;
y = (1 << 9) * x;

Thanks in advance,
Bill


y = scalbn(x,9);

ITYM:

#if FLT_RADIX == 2
y = scalbn(x, 9);
#else
y = ???;
#endif

I've already posted a candidate for "???", one that
eliminates the dependency on C99 and perhaps even
obviates the preprocessor gunk ...

--
Eric.Sosman@xxxxxxx

.

Relevant Pages

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