Re: Simulation of fixed point in c WITH DIFFERENT BIT-WIDTH

[Colin Paul Gloster <Colin_Paul_Gloster@ACM.org>]

Simon Wright posted at Thu, 03 Nov 2005 06:13:19 +0000:

"[..]

I'm not sure what is actually required for portability here. AARM95
3.5.9(22-24) says

   The base range of an ordinary fixed point type need not include the
   specified bounds themselves so that the range specification can be
   given in a natural way, such as:

   type Fraction is delta 2.0**(-15) range -1.0 .. 1.0;

   With 2's complement hardware, such a type could have a signed
   16-bit representation, using 1 bit for the sign and 15 bits for
   fraction, resulting in a base range of -1.0 .. 1.0-2.0**(-15)."

I was unaware of this.

Simon Wright posted at Thu, 03 Nov 2005 06:13:19 +0000:

"[..]
      type F3 is delta 2.0**(-11) range -1.0 .. 1.0 - 2.0**(-11);
      type F4 is delta 2.0**(-14) range -2.0 .. 2.0 - 2.0**(-14);
[..]
[..] the output is
[..]
   F3's size is 12
   F4's size is 16

I'm not sure why F4's size is 16, though; is this a bug?"

No, the size of F4 should be 16 bits. Note that the smallest number F4 
can have is -2.0 as opposed to -1.0.

Remember, on 30 Oct 2005 08:41:38 -0800, Mnamky posted:

"[..]

[..] x is 12-bit wordlength and 11-bit fraction
and b is 16-bit wordlength and 14-bit fraction

[..]"

P.S. I apologize for distorting the References field in 
news:dka579$8fc$1@hudsucker.umdac.umu.se . The second entry in that 
field should of course not have been a copy of the first, but 
news:43653F2C.B20F75B5@fakeaddress.nil instead.