question about float to int type conversion...

• To: netcdf-hdf@xxxxxxxxxxxxxxxx
• Subject: question about float to int type conversion...
• From: Robb Matzke <matzke@xxxxxxxx>
• Date: Mon, 27 Jun 2005 11:06:43 -0400

>>>>> "Ed" == Ed Hartnett <ed@xxxxxxxxxxxxxxxx> writes:
Ed>    float float_data_out2[DIM1_LEN] = {(float)INT_MIN - 1.0, (float)INT_MIN 
- 1.0, (float)INT_MAX + 129.0};

Hi Ed,
  Looking at your output, you're on a machine where
sizeof(float)==sizeof(int)==4. So the initialization of
float_data_out2[] is not doing what you expect. The problem is that
the significand of a float is less than 32 bits (because the sign and
exponent take up some of the other bits). So the +1.0 and -1.0 have
too small a magnitude to make any difference in the arithmetic. The
loss of significant digits can be seen in your output: INT_MIN-1.0
should be -2147483649, not -2147483648.

Ed> So why doesn't it generate an overflow?

Because by time HDF5 gets the data there is no overflow for your first
two array values. Using `double' should fix the problem because it can
represent all 32 bits of an `int'.

-- 
Robb Matzke L-159   | Ph:  812-967-6325  | I/O, I/O, it's off to disk we go,
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National Laboratory | Hrs: 3am-11am PDT  | I/O, I/O.

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  • Re: question about float to int type conversion...
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  • question about float to int type conversion...
    • From: Ed Hartnett