Add overflow support to strtol and clean up the code.
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1df749498a
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5a127a429c
6 changed files with 160 additions and 22 deletions
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@ -24,6 +24,9 @@
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#define STRTOL strtoimax
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#define STRTOL_INT intmax_t
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#define STRTOL_UNSIGNED_INT uintmax_t
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#define STRTOL_INT_MIN INTMAX_MIN
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#define STRTOL_INT_MAX INTMAX_MAX
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#define STRTOL_INT_IS_UNSIGNED false
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#include "../stdlib/strtol.cpp"
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@ -24,6 +24,9 @@
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#define STRTOL strtoumax
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#define STRTOL_INT uintmax_t
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#define STRTOL_UNSIGNED_INT uintmax_t
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#define STRTOL_INT_MIN 0
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#define STRTOL_INT_MAX UINTMAX_MAX
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#define STRTOL_INT_IS_UNSIGNED true
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#include "../stdlib/strtol.cpp"
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@ -25,15 +25,26 @@
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#ifndef STRTOL
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#define STRTOL strtol
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#define STRTOL_INT long
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#define STRTOL_UNSIGNED_INT unsigned long
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#define STRTOL_INT_MIN LONG_MIN
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#define STRTOL_INT_MAX LONG_MAX
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#define STRTOL_INT_IS_UNSIGNED false
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#endif
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#include <assert.h>
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#include <ctype.h>
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#include <errno.h>
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#include <inttypes.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <stdlib.h>
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static int Debase(char c)
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// Nasty, nasty hack to get LLONG_* macros.
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#define __STDC_VERSION__ 199901L
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#include <limits.h>
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// Convert a character into a digit.
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static int debase(char c)
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{
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if ( '0' <= c && c <= '9' )
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return c - '0';
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@ -44,59 +55,171 @@ static int Debase(char c)
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return -1;
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}
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template <class INT, bool UNSIGNED>
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INT ParseInteger(const char* str, char** endptr, int base)
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// Determine whether a multiplication of two integers would overflow/underflow.
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// This is easy if we have a larger integer type, otherwise we'll be creative.
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template <class T_INT,
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bool T_INT_IS_UNSIGNED,
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class T_UNSIGNED_INT,
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T_INT T_INT_MIN,
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T_INT T_INT_MAX>
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static bool would_multiplication_overflow(T_INT a, T_INT b)
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{
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// Prevent accidental divisons by zero in this simple case.
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if ( !a || !b )
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return false;
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// Check if we have a 64-bit integer that it is large enough.
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if ( sizeof(T_INT)*2 <= sizeof(int64_t) )
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{
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int64_t ret_large = (int64_t) a * (int64_t) b;
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return ret_large < (int64_t) T_INT_MIN ||
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(int64_t) T_INT_MAX < ret_large;
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}
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// Check if we have a 128-bit integer that it is large enough.
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#if 64 <= __WORDSIZE
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if ( sizeof(T_INT)*2 <= sizeof(__int128) )
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{
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__int128 ret_large = (__int128) a * (__int128) b;
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return ret_large < (__int128) T_INT_MIN ||
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(__int128) T_INT_MAX < ret_large;
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}
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#endif
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// The fallback strategy is to determine the largest b given a that will not
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// overflow and then see if b is within range. This is trivial if in the
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// unsigned integer case.
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if ( T_INT_IS_UNSIGNED )
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{
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T_INT max_b = a / T_INT_MAX;
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return max_b < b;
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}
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// We have to deal with some cases for signed integers. We'll assume signed
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// integers are in two's complement and use - (unsigned int) value to take
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// the absolute value of a negative value as an unsigned integer in a manner
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// that is defined in C. Whether we use the smallest or largest value depend
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// on whether the sign of a and b is identical.
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else
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{
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T_UNSIGNED_INT a_abs = a < 0 ? - (T_UNSIGNED_INT) a : a;
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T_UNSIGNED_INT b_abs = b < 0 ? - (T_UNSIGNED_INT) b : b;
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T_UNSIGNED_INT min_abs = - (T_UNSIGNED_INT) T_INT_MIN;
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T_UNSIGNED_INT max_abs = T_INT_MAX;
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T_UNSIGNED_INT limit_pos = (0 <= a && 0 <= b) || ( a < 0 && b < 0 );
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T_UNSIGNED_INT limit = limit_pos ? max_abs : min_abs;
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T_UNSIGNED_INT max_b = a_abs / limit;
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return max_b < b_abs;
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}
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}
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extern "C"
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STRTOL_INT STRTOL(const char* restrict str, char** restrict endptr, int base)
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{
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const char* origstr = str;
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int origbase = base;
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while ( isspace(*str) ) { str++; }
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// Skip any leading white space.
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while ( isspace(*str) )
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str++;
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// Reject bad bases.
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if ( base < 0 || 36 < base )
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{
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if ( endptr )
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*endptr = (char*) str;
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return 0;
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return errno = EINVAL, 0;
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}
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INT result = 0;
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bool negative = false;
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char c = *str;
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if ( !UNSIGNED && c == '-' )
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// Handle a leading sign character.
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if ( c == '-' )
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str++, negative = true;
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if ( !UNSIGNED && c == '+' )
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if ( c == '+' )
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str++, negative = false;
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// Autodetect base 8 or base 16.
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if ( !base && str[0] == '0' )
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{
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if ( str[1] == 'x' || str[1] == 'X' )
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str += 2, base = 16;
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else if ( 0 <= Debase(str[1]) && Debase(str[1]) < 8 )
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else if ( 0 <= debase(str[1]) && debase(str[1]) < 8 )
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str++, base = 8;
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}
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// Default to base 10.
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if ( !base )
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base = 10;
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// Skip the leading '0x' prefix in base 16 for hexadecimal integers.
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if ( origbase == 16 && str[0] == '0' && (str[1] == 'x' || str[1] == 'X') )
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str += 2;
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// Determine what value will be returned on overflow/underflow.
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STRTOL_INT overflow_value = negative && !STRTOL_INT_IS_UNSIGNED ?
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STRTOL_INT_MIN :
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STRTOL_INT_MAX;
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// Convert a single character at a time.
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STRTOL_INT result = 0;
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size_t numconvertedchars = 0;
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bool overflow_occured = false;
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while ( (c = *str ) )
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{
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int val = Debase(c);
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if ( val < 0 )
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// Stop if we encounterd a character that doesn't fit in this base.
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int val = debase(c);
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if ( val < 0 || base <= val )
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break;
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if ( base <= val )
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break;
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if ( !UNSIGNED && negative )
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val = -val;
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// TODO: Detect overflow!
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result = result * (INT) base + (INT) val;
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// Attempt to multiply the accumulator with the current base.
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if ( would_multiplication_overflow<STRTOL_INT,
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STRTOL_INT_IS_UNSIGNED,
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STRTOL_UNSIGNED_INT,
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STRTOL_INT_MIN,
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STRTOL_INT_MAX>
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(result, (STRTOL_INT) base) )
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overflow_occured = true, result = overflow_value;
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else
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{
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STRTOL_INT new_result = result * (STRTOL_INT) base;
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assert(result <= new_result);
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result = new_result;
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}
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// Attempt to add the latest digit to the accumulator (positive).
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if ( (STRTOL_INT_IS_UNSIGNED || !negative) &&
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(STRTOL_INT) val <= (STRTOL_INT) (STRTOL_INT_MAX - result) )
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result += (STRTOL_INT) val;
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// Attempt to subtract the latest digit to the accumulator (negative).
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else if ( (!STRTOL_INT_IS_UNSIGNED && negative) &&
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(STRTOL_INT) val <= (STRTOL_INT) (result - STRTOL_INT_MIN) )
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result -= (STRTOL_INT) val;
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// Handle the case where the addition/subtract would overflow/underflow.
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else
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overflow_occured = true, result = overflow_value;
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str++;
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numconvertedchars++;
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}
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// If no characters were successfully converted, rewind to the start, also
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// rewinding past skipped whitespace and sign characters and such.
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if ( !numconvertedchars )
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str = origstr, result = 0;
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// Let the caller know where we got to.
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if ( endptr )
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*endptr = (char*) str;
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// Handle the special case where we are creating an unsigned integer and the
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// string was negative and non-zero and no overflow occured, then we treat
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// it as (the maximum value+1) minus (the negative string as integer).
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if ( STRTOL_INT_IS_UNSIGNED && negative && result && !overflow_occured )
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result = STRTOL_INT_MAX - (result-1);
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return result;
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}
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extern "C" STRTOL_INT STRTOL(const char* str, char** endptr, int base)
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{
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return ParseInteger<STRTOL_INT, STRTOL_INT_IS_UNSIGNED>(str, endptr, base);
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}
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@ -24,6 +24,9 @@
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#define STRTOL strtoll
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#define STRTOL_INT long long
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#define STRTOL_UNSIGNED_INT unsigned long long
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#define STRTOL_INT_MIN LLONG_MIN
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#define STRTOL_INT_MAX LLONG_MAX
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#define STRTOL_INT_IS_UNSIGNED true
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#include "strtol.cpp"
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#define STRTOL strtoul
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#define STRTOL_INT unsigned long
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#define STRTOL_UNSIGNED_INT unsigned long
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#define STRTOL_INT_MIN 0
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#define STRTOL_INT_MAX ULONG_MAX
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#define STRTOL_INT_IS_UNSIGNED true
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#include "strtol.cpp"
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@ -24,6 +24,9 @@
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#define STRTOL strtoull
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#define STRTOL_INT unsigned long long
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#define STRTOL_UNSIGNED_INT unsigned long long
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#define STRTOL_INT_MIN 0
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#define STRTOL_INT_MAX ULLONG_MAX
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#define STRTOL_INT_IS_UNSIGNED true
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#include "strtol.cpp"
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