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For now, solve the precision problem with brute force,

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by using long double where available.
Unfortunately, it won't be available everywhere, so a better solution
would still be nice.
Also, sometimes rounding of smaller sizes doesn't work right yet.
This commit is contained in:
Olaf Seibert
2021-01-18 23:11:00 +01:00
parent 37abe35427
commit 8aea1498c5
3 changed files with 91 additions and 4 deletions
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41
parse.c
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@@ -3,6 +3,7 @@
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <float.h>
#include <ctype.h>
#include "parse.h" /* my own definitions */
@@ -318,6 +319,38 @@ int get_mode(
return TRUE;
}
/*
* We need 56 bits of mantissa.
*
* Try to detect if it is needed, possible and useful to use
* long double instead of double, when parsing floating point numbers.
*/
#if DBL_MANT_DIG >= 56
/* plain double seems big enough */
# define USE_LONG_DOUBLE 0
/* long double exists and seems big enough */
#elif LDBL_MANT_DIG >= 56
# define USE_LONG_DOUBLE 1
#elif defined(LDBL_MANT_DIG)
/* long double exists but is probably still too small */
# define USE_LONG_DOUBLE 1
#else
/* long double does not exist and plain double is too small */
# define USE_LONG_DOUBLE 0
#endif
#if USE_LONG_DOUBLE
# define DOUBLE long double
# define SCANF_FMT "%Lf"
# define FREXP frexpl
#else
# define DOUBLE double
# define SCANF_FMT "%lf"
# define FREXP frexp
#endif
/* Parse PDP-11 64-bit floating point format. */
/* Give a pointer to "size" words to receive the result. */
/* Note: there are probably degenerate cases that store incorrect
@@ -334,8 +367,8 @@ int parse_float(
int size,
unsigned *flt)
{
double d; /* value */
double frac; /* fractional value */
DOUBLE d; /* value */
DOUBLE frac; /* fractional value */
ulong64 ufrac; /* fraction converted to 49 bit
unsigned integer */
int i; /* Number of fields converted by sscanf */
@@ -344,7 +377,7 @@ int parse_float(
unsigned uexp; /* Unsigned excess-128 exponent */
unsigned sign = 0; /* Sign mask */
i = sscanf(cp, "%lf%n", &d, &n);
i = sscanf(cp, SCANF_FMT "%n", &d, &n);
if (i == 0)
return 0; /* Wasn't able to convert */
@@ -359,7 +392,7 @@ int parse_float(
return 1; /* Good job. */
}
frac = frexp(d, &sexp); /* Separate into exponent and mantissa */
frac = FREXP(d, &sexp); /* Separate into exponent and mantissa */
if (sexp < -127 || sexp > 127)
return 0; /* Exponent out of range. */