[Cfp-interest 1728] Re: AI about macro for array size in example
Mike Cowlishaw
mfc at speleotrove.com
Sun Jul 26 09:49:04 PDT 2020
Yes, tricky. STRLEN is one less that the needed constant, too. In fact,
in my code, I actually use:
#define INTLEN 11 // length needed for an ASCII'd Int
// this is from a shared .h; Int is 32-bit int
.. I never
// never use raw 'int' in my code and in fact
in that .h have:
// #define Int int32_t
// #define int ?
// to ensure that I don't [I still have a lot
of 8-bit and 16-bit
// code/platforms to test on]
// then ...
char buffer[INTLEN+1]; // i.e., the space for the null char is added
here so is explicit
So, perhaps
#define MAXHEXCHARS 40
...
char s[MAXHEXCHARS+1];
... but maybe we're spending too much time on this :-). Your call.
_____
From: Jim Thomas [mailto:jaswthomas at sbcglobal.net]
Sent: 25 July 2020 23:18
To: Mike Cowlishaw
Cc: CFP
Subject: Re: [Cfp-interest 1718] AI about macro for array size in example
Id like to avoid alluding to the size of a string. Its really a size
greater than the lengths of the hex strings, which is what is needed for the
array size. The C standard uses maxsize for parameters with this meaning.
How about
#define MAXSIZE 41 // > intermediate hex string length
- Jim Thomas
On Jul 24, 2020, at 6:36 AM, Mike Cowlishaw <mfc at speleotrove.com> wrote:
Looks good. Maybe MAXSTRSIZE? (S on its own is a bit mysterious, and it's
not clear how to pronounce it).
Mike
_____
From: Cfp-interest [mailto:cfp-interest-bounces at oakapple.net] On Behalf Of
Jim Thomas
Sent: 24 July 2020 00:33
To: CFP
Subject: [Cfp-interest 1718] AI about macro for array size in example
Action item:
Jim: For cfp3x-annex-20200706.pdf, Annex X, new example (page 33),
change the magic number 40 (which needs to be verified) to be a macro and
add in a descriptive definition of that macro.
Oops. 41 instead of 40. How does the following look?
- Jim Thomas
+++++++++++++++++++++++++++
[4] EXAMPLE If the IEC 60559 binary128 format is supported as a
non-arithmetic format, data in binary128 format can be converted to type
_Decimal128 as follows:
#define __STDC_WANT_IEC_60559_TYPES_EXT__
#include <stdlib.h>
#define MAXSSIZE 41 // of intermediate hexadecimal string
unsigned char b128[16]; // for input binary128 datum
_Decimal128 d128; // for result
char s[MAXSSIZE];
// store input binary128 datum in array b128
...
strfromencf128(s, MAXSSIZE, %a, b128);
d128 = strtod128(s, NULL);
...
Use of %a for formatting assures an exact conversion of the value in
binary format to character sequence. The value of that character sequence
will be correctly rounded to _Decimal128, as specified above in this
subclause. The array s for the output of strfromencf128 need have no greater
size than 41, which is the maximum length of strings of the form
[-]0xh.h
hp±d, where there are up to 29 hexadecimal digits h and d has 5
digits
plus 1 for the null character.
+++++++++++++++++++++++++++
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