Talk:IBM Floating Point Architecture
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This page, aside from being badly written, is misleading. As far as I can tell, what it is trying to describe is the floating-point format used by IBM's S/390 hardware, whose fp format dates back to the System/360 of the 1960s, and may also be similar to a 56-bit mantissa format used by some VAX machines. On the other hand, IBM POWER chips use the IEEE 754 format, and I can't find any reference to support the idea that the S/390 format is named the IBM Floating Point Standard. —Steven G. Johnson 21:25, 19 Mar 2004 (UTC)
- Agreed. I have tidied it up a bit; the information down to the code section is useful and was basically correct, however. It should be renamed 'IBM Floating Point Architecture' .. is there an easy way to rename a Wikipedia page and all references to it? mfc 08:57, 20 Mar 2004 (UTC)
- (Ah, rename is called 'move'. Done. mfc 08:15, 23 Mar 2004 (UTC))
- The article by Gerwig et al. in the IBM Systems Journal 48(3) May/July 2004 refers to it as the "zSeries/trademark hexadecimal floating-point architecture (HFP)".
(Also, Wikipedia is not a code repository; the Java snippet is probably inappropriate, even if it is not a copyright infringement. Steven G. Johnson)
- Agreed. Suggest commenting it out, or move it to here? mfc
One reason we still care about this format has been added. The code has been replaced with an algorithm, that I think could be valuable. --Tumb 22:01, 22 Mar 2004 (UTC)
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[edit] Name
This article is specifically about IBM System/360 (et seq.) architecture floating-point, not about IBM in general. So the name should be changed. --Macrakis 17:44, 17 Apr 2005 (UTC)
[edit] Comparison to 754
Article says "hexadecimal floating-point uses a similar approach to IEEE 754 binary floating-point", but 360 FP is different from IEEE FP in almost every way that two FP formats can differ: different radix, different exponent range, different significand precision and range (360 is 1/16<=c<1, IEEE is 1<=c<2), no hidden bit, no special values (NaN, Inf, etc.), different rounding behavior. Also, didn't 360 also support single-precision FP (and quad?)? --Macrakis 17:44, 17 Apr 2005 (UTC)
[edit] 360 FP
The 360 floating point is always normalized, so that the leftmost hex digit of the significand is nonzero. This gives each size (single, double, quad) a variable-precision behavior that can be annoying. The single-precision 360 FP, for example, can have as little as 21 bits precision in its significand, or as much as 24 bits. This is particularly vexing when one must account for all the bits while converting from 360 FP to IEEE 754 and vice versa.
[edit] Representation of zero
The standard representation of zero is missing. Probably it's 0x40000000, but I don't know. --84.150.204.140 02:04, 8 June 2006 (UTC)
- After thinking about it, 0x00000000 makes more sense, and that's what I found in GRIB files. --84.150.204.140 02:14, 8 June 2006 (UTC)
