Re: [Psidev-ms-dev] Why base64?

[Mike C. <tu...@gm...>]

[This message seems to have been bounced by Sourceforge, so I'm
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On 9/28/06, Mike Coleman <tu...@gm...> wrote:
> Makes sense.  To put it in other words, there are two questions here:
>
> 1.  Are the values represented as base64-encoded bitstrings or as ASCII text?
>
> 2.  Should the values be rounded to the precision of the instrument
> (probably plus a digit, etc.), or should an arbitrary number of
> figures be used?  Again, this isn't about losing information, as we're
> only discussing rounding away noise.
>
> These two questions are entirely orthogonal, as far as I can see, and
> it would be possible to allow both options for both questions, if this
> were seen as being worthwhile.  The one interaction is that if you use
> the ASCII text encoding, rounding the figures will make the mzData
> file smaller.
>
> Regarding ambiguity, the ASCII text representation would allow
> differing whitespace (which produce no semantic difference).  I guess
> the base64 encoding also allows differing surrounding whitespace.
>
> With respect to the base64 encoding, one corner case comes to mind.
> Are special IEEE values like NaN, the infinities, negative zero, etc.,
> allowed?  If so, what should the interpretation be?
>
> Mike
>
>
> The example code I mentioned:
>
> /* gcc -g -O2 -ffloat-store -o ieee-test ieee-test.c */
>
> /* strtof is GNU/C99 */
> #define _GNU_SOURCE
>
> #include <assert.h>
> #include <errno.h>
> #include <limits.h>
> #include <stdio.h>
> #include <stdlib.h>
>
>
> union bits {
>   unsigned int u;
>   float f;
> };
>
>
> int
> main() {
>   unsigned int i;
>   union bits x, x2;
>   int zeros_seen = 0;
>
>   assert(sizeof x.u == sizeof x.f);
>   assert(&x.u == &x.f);
>
>
>
>   for (i=0; ; i++) {
>     char buf[128];
>
>     if (i == 0)
>       if (++zeros_seen > 1)
>         break;
>
> #if 0
>     if (!(i % 100000))
>       putc('.', stderr);
> #endif
>
>     x.u = i;
>     if (x.f != x.f)
>       continue;                 /* skip error values */
>
>     sprintf(buf, "%.8e", x.f);
>
>     errno = 0;
>     x2.f = strtof(buf, 0);
>     if (errno == ERANGE) {
>       printf("strtof error for %s\n", buf);
>       continue;
>     }
>
>     if (x2.u != x.u)
>       printf("bit difference for %s (%u != %u)\n", buf, x2.u, x.u);
>   }
> }
>