Talk:IBM hexadecimal floating-point

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Misleading

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

Algorithm instead of code

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)

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)

This article should be renamed to reflect the name of the floating point format, which is I believe base-16 excess-64 floating point format, possibly in a different order 81.187.162.109 08:33, 15 July 2007 (UTC).[reply]

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)

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.

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)[reply]

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)[reply]

i think it is terrible

The deferent format of data bings a great difficults in our daily works. it is time to do something to stop it . —Preceding unsigned comment added by 124.17.4.30 (talk) 09:31, 17 July 2008 (UTC)[reply]

Bit Order or Endianness

The first two references (IBM System/360/370 Principles of Operation) state quite clearly that bit 0 is the sign. For example the 360 document says on page 12: "Bit position 0 in either [short or long] format is the sign (S) of the fraction". I suggest that this be corrected in the ASCII-Art diagrams. --130.75.243.201 (talk) 16:19, 25 April 2012 (UTC)[reply]

Unlike everyone else, IBM numbers bits from left to right, so what IBM calls "bit 0" is the leftmost (most significant) bit within a word. — Loadmaster (talk) 17:37, 10 February 2014 (UTC)[reply]

Yet the article has this self-contradictory note: "Note that IBM documentation numbers the bits from right to left, so that the most significant bit is designated as bit number 0."

I added that note, and I just corrected it; thanks for catching it. Hopefully it is clear that IBM names the bits the opposite way of what practically everyone else does, thus what IBM calls bit 0 is the most significant (left-most) bit of a word. — Loadmaster (talk) 19:55, 30 May 2014 (UTC)[reply]

Representation of 0.1

Is the representation of 0.1 given in the article correct? The article gives:

S Exp Fraction 0 100 0000 0001 1001 1001 1001 1001 1010

where the rightmost nybble is 1010 rather than the recurring 1001.

This could be a mistake or is the rounding up from 1001 to 1010 intentional and necessary? — Preceding unsigned comment added by 89.11.138.63 (talk) 10:43, 21 October 2014 (UTC)[reply]

10011001 rounded to 4 binary digits is 1010, since 1001 > 1000. --Macrakis (talk) 14:10, 21 October 2014 (UTC)[reply]