From: Dave Peterson <davep@acm.org>

Date: Thu, 29 Nov 2001 13:25:22 -0500

Message-Id: <a05010403b82c2b0178ff@[146.115.112.32]>

To: "Ashok Malhotra" <ashokma@microsoft.com>, <www-xml-schema-comments@w3.org>

Date: Thu, 29 Nov 2001 13:25:22 -0500

Message-Id: <a05010403b82c2b0178ff@[146.115.112.32]>

To: "Ashok Malhotra" <ashokma@microsoft.com>, <www-xml-schema-comments@w3.org>

At 9:50 AM -0800 11/29/01, Ashok Malhotra wrote: >It has been brought to my attention that there may be an error in >the specification of the canonical lexical form for float/double. >The current specification for float is below. Double is similar. >A proposed resolution to this potential errata is to amend the above >text after the colon as follows: > >number representations must be normalized such that there is a >single non-zero digit to the left of the decimal point and at least >a single digit to the right of the decimal point. Zero is >represented by '0.0E1' and '-0.0E1'. > >My one concern is that to represent very large numbers it may not be >possible to have just a single number to the left of the decimal >point in the mantissa. This needs to be checked. Dave P, can you >help here? There is no limit specified in the Rec for the number of digits in an integer numeral, which is what the exponent part is constrained to be. Therefore, a very large negative integer can always be selected which shifts the decimal point enough to give a single digit to the left of the decimal of the "mantissa" (which, by the way, is a misuse of the word "mantissa"). Warning: Unlike most datatypes, decimal and double have a lexical space which ordinarily would be taken to include numerals naming values that are not in the value space; rather, they are taken to name the nearest value that *is* in the value space. If the value space is restricted, say to values representable with fewer bits for exponent or "mantissa", then the numerals originally mapping to the dropped values will *not* map to the nearest remaining value; they will drop from the lexical space. I have no idea under what circumstances this will, as they say, "screw the pooch". -- Dave Peterson SGMLWorks! davep@acm.orgReceived on Thursday, 29 November 2001 13:27:51 UTC

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