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Better calcuation of dec string width (Larry Doolittle)

This commit is contained in:
steve 2002-01-22 00:18:10 +00:00
parent fcf64c0c38
commit 4f28f6a770
1 changed files with 42 additions and 20 deletions
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62
vpi/sys_display.c
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@ -17,7 +17,7 @@
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#if !defined(WINNT) && !defined(macintosh)
#ident "$Id: sys_display.c,v 1.33 2002/01/15 03:23:34 steve Exp $"
#ident "$Id: sys_display.c,v 1.34 2002/01/22 00:18:10 steve Exp $"
#endif
# include "config.h"
@ -36,13 +36,43 @@ struct strobe_cb_info {
unsigned nitems;
};
static int calc_dec_size(int nr_bits)
// The number of decimal digits needed to represent a
// nr_bits binary number is floor(nr_bits*log_10(2))+1,
// where log_10(2) = 0.30102999566398.... and I approximate
// this transcendental number as 146/485, to avoid the vagaries
// of floating-point. The smallest nr_bits for which this
// approximation fails is 2621,
// 2621*log_10(2)=789.9996, but (2621*146+484)/485=790 (exactly).
// In cases like this, all that happens is we allocate one
// unneeded char for the output. I add a "L" suffix to 146
// to make sure the computation is done as long ints, otherwise
// on a 16-bit int machine (allowed by ISO C) we would mangle
// this computation for bit-length of 224. I'd like to put
// in a test for nr_bits < LONG_MAX/146, but don't know how
// to fail, other than crashing.
//
// In an April 2000 thread in comp.unix.programmer, with subject
// "integer -> string", I <LRDoolittle@lbl.gov> give the 28/93
// approximation, but overstate its accuracy: that version first
// fails when the number of bits is 289, not 671.
//
// This result does not include space for a trailing '\0', if any.
//
inline static int calc_dec_size(int nr_bits, int is_signed)
{
// over-the-top accuracy... :-)
//
// nr of bits = floor(log10(2^nr_bits) + 1.0)
// = floor(nr_bits * ln(2)/ln(10) + 1.0)
return (int)( ((double)nr_bits) * 0.301029996 + 1.0);
int r;
if (is_signed) --nr_bits;
r = (nr_bits * 146L + 484) / 485;
if (is_signed) ++r;
return r;
}
static int vpi_get_dec_size(vpiHandle item)
{
return calc_dec_size(
vpi_get(vpiSize, item),
vpi_get(vpiSigned, item)==1
);
}
static void array_from_iterator(struct strobe_cb_info*info, vpiHandle argv)
@ -271,14 +301,7 @@ static int format_str(vpiHandle scope, unsigned int mcd,
// simple %d parameter.
// Size is now determined by the width
// of the vector or integer
fsize = vpi_get(vpiSize, argv[idx]);
fsize = calc_dec_size(fsize);
if ( vpi_get(vpiSigned, argv[idx]) ==1){
// Pure integers need one more position
// for an optional '-' bit
fsize++;
}
fsize = vpi_get_dec_size(argv[idx]);
}
vpi_mcd_printf(mcd, "%*s", fsize,
@ -423,11 +446,7 @@ static void do_display(unsigned int mcd, struct strobe_cb_info*info)
switch(info->default_format){
case vpiDecStrVal:
size = vpi_get(vpiSize, item);
size = calc_dec_size(size);
if ( vpi_get(vpiSigned, item) ==1){
size++;
}
size = vpi_get_dec_size(item);
vpi_mcd_printf(mcd, "%*s", size, value.value.str);
break;
@ -1102,6 +1121,9 @@ void sys_display_register()
/*
* $Log: sys_display.c,v $
* Revision 1.34 2002/01/22 00:18:10 steve
* Better calcuation of dec string width (Larry Doolittle)
*
* Revision 1.33 2002/01/15 03:23:34 steve
* Default widths pad out as per the standard,
* add $displayb/o/h et al., and some better