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stdlib: add and test strtold (DONE)

The method is rather naive - digits read as an integer, then multipled
by a power of 10 or 2. This does not always give exact results, but it's
close enough for now. A stub support for long double larger than 64 bits
is provided.
master
Lephenixnoir 8 months ago
parent
commit
efb37cf783
Signed by: Lephenixnoir GPG Key ID: 1BBA026E13FC0495
  1. 1
      CMakeLists.txt
  2. 3
      STATUS
  3. 193
      src/libc/stdlib/strtold.c

1
CMakeLists.txt

@ -121,6 +121,7 @@ set(SOURCES
src/libc/stdlib/reallocarray.c
src/libc/stdlib/strto_int.c
src/libc/stdlib/strtol.c
src/libc/stdlib/strtold.c
src/libc/stdlib/strtoll.c
src/libc/stdlib/strtoul.c
src/libc/stdlib/strtoull.c

3
STATUS

@ -89,7 +89,8 @@ DONE: Function/symbol/macro is defined, builds, links, and is tested
7.20 <stdlib.h>
! 7.20.1.1 atof: TODO
7.20.1.2 atoi, atol, atoll: DONE
! 7.20.1.3 strtod, strtof, strtold: TODO
! 7.20.1.3 strtod, strtof: TODO
strtold: DONE
7.20.1.4 strtol, strtoul, strtoll, strtoull: DONE
! 7.20.2 Pseudo-random sequence generation functions: TODO
! 7.20.3 Memory management functions: TODO (check existing code first)

193
src/libc/stdlib/strtold.c

@ -0,0 +1,193 @@
#include <stdlib.h>
#include <stdbool.h>
#include <float.h>
#include <fenv.h>
#include <math.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
/*
** In the following conversions, the significant digits are represented in an
** integer and multiplied at the last moment by a suitable power of 10 (decimal
** representation) or 2 (hexadecimal representation). An integer of a suitable
** size needs to be used; that size is the size of the long double type.
**
** TODO: vhex-x86: Using 128-bit long double is untested!
*/
#if __SIZEOF_LONG_DOUBLE__ == 8
# define SIGNIFICAND_TYPE uint64_t
# define SIGNIFICAND_DIGITS 17
#elif __SIZEOF_LONG_DOUBLE__ <= 16
# define SIGNIFICAND_TYPE unsigned __int128
# define SIGNIFICAND_DIGITS 38
#else
# error long double larger than 128 bits is not supported
#endif
/* Basically strncasecmp. */
static int ncasecmp(char const *left, char const *right, size_t n)
{
for(size_t i = 0; i < n; i++) {
int diff = tolower(left[i]) - tolower(right[i]);
if(diff) return diff;
}
return 0;
}
/*
** Parse digits and exponent into integers, in decimal or hexadecimal notation.
**
** -> In decimal notation; we read up to 19 (64-bit) or 38 (128-bit) digits,
* which is enough to fill the mantissa of a long double, and later multiply
** the digits by a power of 10. The main approximation is the power of 10.
**
** -> In hexadecimal notation, we read as many bits as the mantissa of a long
** double, then later multiply by a power of 2. There are no approximations.
*/
static void parse_digits(char const * restrict *ptr0, bool *valid,
SIGNIFICAND_TYPE *digits, long *exponent, bool hexadecimal)
{
char const *ptr = *ptr0;
bool dot_found = false;
int digits_found = 0;
*digits = 0;
*exponent = 0;
int max_digits = hexadecimal ? LDBL_MANT_DIG / 4 : SIGNIFICAND_DIGITS;
/* TODO: locale: use a locale-aware decimal separator */
int dot_character = '.';
int exp_character = (hexadecimal ? 'p' : 'e');
for(int i = 0; isdigit(*ptr) || (hexadecimal && isxdigit(*ptr))
|| *ptr == dot_character; i++, ptr++) {
/* Allow only one dot in the string, stop at the second one */
if(*ptr == dot_character && dot_found) break;
if(*ptr == dot_character) {
dot_found = true;
continue;
}
/* Count digits only until SIGNIFICAND_DIGITS */
if(digits_found < max_digits) {
if(hexadecimal) {
int v = *ptr - '0';
if(!isdigit(*ptr)) v = tolower(*ptr)-'a'+10;
*digits = (*digits << 4) + v;
}
else {
*digits = (*digits * 10) + (*ptr - '0');
}
}
else (*exponent)++;
if(dot_found) (*exponent)--;
/* But also round at the first discarded one */
if(digits_found == max_digits && *ptr >= '5')
(*digits)++;
digits_found++;
}
/* Require at least one digit to be present; if not, the whole string
is considered invalid */
if(!digits_found) {
*valid = false;
return;
}
/* In hexadecimal, each character is worth 4 bits of exponent */
if(hexadecimal) (*exponent) *= 4;
/* Parse exponent */
if(tolower(*ptr) == exp_character) {
char *end;
long e = strtol(ptr + 1, &end, 10);
/* If an integer cannot be parsed, ignore the 'e...' part */
if(end != ptr + 1) {
ptr = end;
*exponent += e;
}
}
*ptr0 = ptr;
*valid = true;
}
long double strtold(char const * restrict ptr, char ** restrict endptr)
{
/* Save the value of ptr in endptr, in case format is invalid */
if(endptr) *endptr = (char *)ptr;
/* Skip initial whitespace */
while(isspace(*ptr)) ptr++;
/* Read optional sign */
bool negative = false;
if(*ptr == '-') negative = true;
if(*ptr == '-' || *ptr == '+') ptr++;
/* Result variable */
bool valid = true;
long double x = 0.0;
/* NaN possibly with an argument */
if(!ncasecmp(ptr, "nan", 3)) {
if(ptr[3] == '(') {
x = __builtin_nanl(ptr+4);
while(*ptr != ')') ptr++;
}
else {
x = __builtin_nanl("");
ptr += 3;
}
}
/* Infinity */
else if(!ncasecmp(ptr, "infinity", 8)) {
x = __builtin_infl();
ptr += 8;
}
else if(!ncasecmp(ptr, "inf", 3)) {
x = __builtin_infl();
ptr += 3;
}
else {
SIGNIFICAND_TYPE digits = 0;
long exponent = 0;
if(ptr[0] == '0' && tolower(ptr[1]) == 'x') {
ptr += 2;
parse_digits(&ptr, &valid, &digits, &exponent, true);
x = (long double)digits * exp2(exponent);
}
else {
parse_digits(&ptr, &valid, &digits, &exponent, false);
x = (long double)digits * powl(10, exponent);
}
/*
** Detect overflow, somewhat. Implementation is not required to
** set errno on underflow, which makes things much easier for
** us as underflow gives 0 (7.20.1.3§10).
*/
if(x == HUGE_VALL) {
errno = ERANGE;
}
}
/* Apply sign; this method is allowed by 7.20.1.3§4.249 */
if(negative) x = -x;
/* Save the result pointer */
if(endptr && valid) *endptr = (char *)ptr;
return x;
}
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