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Add overflow support to strtol and clean up the code.

This commit is contained in:
Jonas 'Sortie' Termansen 2013-07-19 19:58:21 +02:00
parent 1df749498a
commit 5a127a429c
6 changed files with 160 additions and 22 deletions
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3
libc/inttypes/strtoimax.cpp
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@ -24,6 +24,9 @@
#define STRTOL strtoimax
#define STRTOL_INT intmax_t
#define STRTOL_UNSIGNED_INT uintmax_t
#define STRTOL_INT_MIN INTMAX_MIN
#define STRTOL_INT_MAX INTMAX_MAX
#define STRTOL_INT_IS_UNSIGNED false
#include "../stdlib/strtol.cpp"

3
libc/inttypes/strtoumax.cpp
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@ -24,6 +24,9 @@
#define STRTOL strtoumax
#define STRTOL_INT uintmax_t
#define STRTOL_UNSIGNED_INT uintmax_t
#define STRTOL_INT_MIN 0
#define STRTOL_INT_MAX UINTMAX_MAX
#define STRTOL_INT_IS_UNSIGNED true
#include "../stdlib/strtol.cpp"

167
libc/stdlib/strtol.cpp
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@ -25,15 +25,26 @@
#ifndef STRTOL
#define STRTOL strtol
#define STRTOL_INT long
#define STRTOL_UNSIGNED_INT unsigned long
#define STRTOL_INT_MIN LONG_MIN
#define STRTOL_INT_MAX LONG_MAX
#define STRTOL_INT_IS_UNSIGNED false
#endif
#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <inttypes.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
static int Debase(char c)
// Nasty, nasty hack to get LLONG_* macros.
#define __STDC_VERSION__ 199901L
#include <limits.h>
// Convert a character into a digit.
static int debase(char c)
{
if ( '0' <= c && c <= '9' )
return c - '0';
@ -44,59 +55,171 @@ static int Debase(char c)
return -1;
}
template <class INT, bool UNSIGNED>
INT ParseInteger(const char* str, char** endptr, int base)
// Determine whether a multiplication of two integers would overflow/underflow.
// This is easy if we have a larger integer type, otherwise we'll be creative.
template <class T_INT,
bool T_INT_IS_UNSIGNED,
class T_UNSIGNED_INT,
T_INT T_INT_MIN,
T_INT T_INT_MAX>
static bool would_multiplication_overflow(T_INT a, T_INT b)
{
// Prevent accidental divisons by zero in this simple case.
if ( !a || !b )
return false;
// Check if we have a 64-bit integer that it is large enough.
if ( sizeof(T_INT)*2 <= sizeof(int64_t) )
{
int64_t ret_large = (int64_t) a * (int64_t) b;
return ret_large < (int64_t) T_INT_MIN ||
(int64_t) T_INT_MAX < ret_large;
}
// Check if we have a 128-bit integer that it is large enough.
#if 64 <= __WORDSIZE
if ( sizeof(T_INT)*2 <= sizeof(__int128) )
{
__int128 ret_large = (__int128) a * (__int128) b;
return ret_large < (__int128) T_INT_MIN ||
(__int128) T_INT_MAX < ret_large;
}
#endif
// The fallback strategy is to determine the largest b given a that will not
// overflow and then see if b is within range. This is trivial if in the
// unsigned integer case.
if ( T_INT_IS_UNSIGNED )
{
T_INT max_b = a / T_INT_MAX;
return max_b < b;
}
// We have to deal with some cases for signed integers. We'll assume signed
// integers are in two's complement and use - (unsigned int) value to take
// the absolute value of a negative value as an unsigned integer in a manner
// that is defined in C. Whether we use the smallest or largest value depend
// on whether the sign of a and b is identical.
else
{
T_UNSIGNED_INT a_abs = a < 0 ? - (T_UNSIGNED_INT) a : a;
T_UNSIGNED_INT b_abs = b < 0 ? - (T_UNSIGNED_INT) b : b;
T_UNSIGNED_INT min_abs = - (T_UNSIGNED_INT) T_INT_MIN;
T_UNSIGNED_INT max_abs = T_INT_MAX;
T_UNSIGNED_INT limit_pos = (0 <= a && 0 <= b) || ( a < 0 && b < 0 );
T_UNSIGNED_INT limit = limit_pos ? max_abs : min_abs;
T_UNSIGNED_INT max_b = a_abs / limit;
return max_b < b_abs;
}
}
extern "C"
STRTOL_INT STRTOL(const char* restrict str, char** restrict endptr, int base)
{
const char* origstr = str;
int origbase = base;
while ( isspace(*str) ) { str++; }
// Skip any leading white space.
while ( isspace(*str) )
str++;
// Reject bad bases.
if ( base < 0 || 36 < base )
{
if ( endptr )
*endptr = (char*) str;
return 0;
return errno = EINVAL, 0;
}
INT result = 0;
bool negative = false;
char c = *str;
if ( !UNSIGNED && c == '-' )
// Handle a leading sign character.
if ( c == '-' )
str++, negative = true;
if ( !UNSIGNED && c == '+' )
if ( c == '+' )
str++, negative = false;
// Autodetect base 8 or base 16.
if ( !base && str[0] == '0' )
{
if ( str[1] == 'x' || str[1] == 'X' )
str += 2, base = 16;
else if ( 0 <= Debase(str[1]) && Debase(str[1]) < 8 )
else if ( 0 <= debase(str[1]) && debase(str[1]) < 8 )
str++, base = 8;
}
// Default to base 10.
if ( !base )
base = 10;
// Skip the leading '0x' prefix in base 16 for hexadecimal integers.
if ( origbase == 16 && str[0] == '0' && (str[1] == 'x' || str[1] == 'X') )
str += 2;
// Determine what value will be returned on overflow/underflow.
STRTOL_INT overflow_value = negative && !STRTOL_INT_IS_UNSIGNED ?
STRTOL_INT_MIN :
STRTOL_INT_MAX;
// Convert a single character at a time.
STRTOL_INT result = 0;
size_t numconvertedchars = 0;
bool overflow_occured = false;
while ( (c = *str ) )
{
int val = Debase(c);
if ( val < 0 )
// Stop if we encounterd a character that doesn't fit in this base.
int val = debase(c);
if ( val < 0 || base <= val )
break;
if ( base <= val )
break;
if ( !UNSIGNED && negative )
val = -val;
// TODO: Detect overflow!
result = result * (INT) base + (INT) val;
// Attempt to multiply the accumulator with the current base.
if ( would_multiplication_overflow<STRTOL_INT,
STRTOL_INT_IS_UNSIGNED,
STRTOL_UNSIGNED_INT,
STRTOL_INT_MIN,
STRTOL_INT_MAX>
(result, (STRTOL_INT) base) )
overflow_occured = true, result = overflow_value;
else
{
STRTOL_INT new_result = result * (STRTOL_INT) base;
assert(result <= new_result);
result = new_result;
}
// Attempt to add the latest digit to the accumulator (positive).
if ( (STRTOL_INT_IS_UNSIGNED || !negative) &&
(STRTOL_INT) val <= (STRTOL_INT) (STRTOL_INT_MAX - result) )
result += (STRTOL_INT) val;
// Attempt to subtract the latest digit to the accumulator (negative).
else if ( (!STRTOL_INT_IS_UNSIGNED && negative) &&
(STRTOL_INT) val <= (STRTOL_INT) (result - STRTOL_INT_MIN) )
result -= (STRTOL_INT) val;
// Handle the case where the addition/subtract would overflow/underflow.
else
overflow_occured = true, result = overflow_value;
str++;
numconvertedchars++;
}
// If no characters were successfully converted, rewind to the start, also
// rewinding past skipped whitespace and sign characters and such.
if ( !numconvertedchars )
str = origstr, result = 0;
// Let the caller know where we got to.
if ( endptr )
*endptr = (char*) str;
// Handle the special case where we are creating an unsigned integer and the
// string was negative and non-zero and no overflow occured, then we treat
// it as (the maximum value+1) minus (the negative string as integer).
if ( STRTOL_INT_IS_UNSIGNED && negative && result && !overflow_occured )
result = STRTOL_INT_MAX - (result-1);
return result;
}
extern "C" STRTOL_INT STRTOL(const char* str, char** endptr, int base)
{
return ParseInteger<STRTOL_INT, STRTOL_INT_IS_UNSIGNED>(str, endptr, base);
}

3
libc/stdlib/strtoll.cpp
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@ -24,6 +24,9 @@
#define STRTOL strtoll
#define STRTOL_INT long long
#define STRTOL_UNSIGNED_INT unsigned long long
#define STRTOL_INT_MIN LLONG_MIN
#define STRTOL_INT_MAX LLONG_MAX
#define STRTOL_INT_IS_UNSIGNED true
#include "strtol.cpp"

3
libc/stdlib/strtoul.cpp
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@ -24,6 +24,9 @@
#define STRTOL strtoul
#define STRTOL_INT unsigned long
#define STRTOL_UNSIGNED_INT unsigned long
#define STRTOL_INT_MIN 0
#define STRTOL_INT_MAX ULONG_MAX
#define STRTOL_INT_IS_UNSIGNED true
#include "strtol.cpp"

3
libc/stdlib/strtoull.cpp
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@ -24,6 +24,9 @@
#define STRTOL strtoull
#define STRTOL_INT unsigned long long
#define STRTOL_UNSIGNED_INT unsigned long long
#define STRTOL_INT_MIN 0
#define STRTOL_INT_MAX ULLONG_MAX
#define STRTOL_INT_IS_UNSIGNED true
#include "strtol.cpp"