js/src/jsnum.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef jsnum_h
#define jsnum_h

#include "mozilla/FloatingPoint.h"
#include "mozilla/Range.h"

#include "NamespaceImports.h"

#include "js/Conversions.h"

#include "vm/StringType.h"

// This macro is should be `one' if current compiler supports builtin functions
// like __builtin_sadd_overflow.
#if __GNUC__ >= 5
// GCC 5 and above supports these functions.
#define BUILTIN_CHECKED_ARITHMETIC_SUPPORTED(x) 1
#else
// For CLANG, we use its own function to check for this.
#ifdef __has_builtin
#define BUILTIN_CHECKED_ARITHMETIC_SUPPORTED(x) __has_builtin(x)
#endif
#endif
#ifndef BUILTIN_CHECKED_ARITHMETIC_SUPPORTED
#define BUILTIN_CHECKED_ARITHMETIC_SUPPORTED(x) 0
#endif

namespace js {

class StringBuffer;

extern MOZ_MUST_USE bool InitRuntimeNumberState(JSRuntime* rt);

#if !EXPOSE_INTL_API
extern void FinishRuntimeNumberState(JSRuntime* rt);
#endif

/* Initialize the Number class, returning its prototype object. */
extern JSObject* InitNumberClass(JSContext* cx, HandleObject obj);

/*
 * When base == 10, this function implements ToString() as specified by
 * ECMA-262-5 section 9.8.1; but note that it handles integers specially for
 * performance.  See also js::NumberToCString().
 */
template <AllowGC allowGC>
extern JSString* NumberToString(JSContext* cx, double d);

extern JSAtom* NumberToAtom(JSContext* cx, double d);

template <AllowGC allowGC>
extern JSFlatString* Int32ToString(JSContext* cx, int32_t i);

extern JSAtom* Int32ToAtom(JSContext* cx, int32_t si);

// ES6 15.7.3.12
extern bool IsInteger(const Value& val);

/*
 * Convert an integer or double (contained in the given value) to a string and
 * append to the given buffer.
 */
extern MOZ_MUST_USE bool JS_FASTCALL
NumberValueToStringBuffer(JSContext* cx, const Value& v, StringBuffer& sb);

extern JSFlatString* IndexToString(JSContext* cx, uint32_t index);

/*
 * Usually a small amount of static storage is enough, but sometimes we need
 * to dynamically allocate much more.  This struct encapsulates that.
 * Dynamically allocated memory will be freed when the object is destroyed.
 */
struct ToCStringBuf {
  /*
   * The longest possible result that would need to fit in sbuf is
   * (-0x80000000).toString(2), which has length 33.  Longer cases are
   * possible, but they'll go in dbuf.
   */
  static const size_t sbufSize = 34;
  char sbuf[sbufSize];
  char* dbuf;

  ToCStringBuf();
  ~ToCStringBuf();
};

/*
 * Convert a number to a C string.  When base==10, this function implements
 * ToString() as specified by ECMA-262-5 section 9.8.1.  It handles integral
 * values cheaply.  Return nullptr if we ran out of memory.  See also
 * NumberToCString().
 */
extern char* NumberToCString(JSContext* cx, ToCStringBuf* cbuf, double d,
                             int base = 10);

/*
 * The largest positive integer such that all positive integers less than it
 * may be precisely represented using the IEEE-754 double-precision format.
 */
const double DOUBLE_INTEGRAL_PRECISION_LIMIT = uint64_t(1) << 53;

/*
 * Parse a decimal number encoded in |chars|.  The decimal number must be
 * sufficiently small that it will not overflow the integrally-precise range of
 * the double type -- that is, the number will be smaller than
 * DOUBLE_INTEGRAL_PRECISION_LIMIT
 */
template <typename CharT>
extern double ParseDecimalNumber(const mozilla::Range<const CharT> chars);

/*
 * Compute the positive integer of the given base described immediately at the
 * start of the range [start, end) -- no whitespace-skipping, no magical
 * leading-"0" octal or leading-"0x" hex behavior, no "+"/"-" parsing, just
 * reading the digits of the integer.  Return the index one past the end of the
 * digits of the integer in *endp, and return the integer itself in *dp.  If
 * base is 10 or a power of two the returned integer is the closest possible
 * double; otherwise extremely large integers may be slightly inaccurate.
 *
 * If [start, end) does not begin with a number with the specified base,
 * *dp == 0 and *endp == start upon return.
 */
template <typename CharT>
extern MOZ_MUST_USE bool GetPrefixInteger(JSContext* cx, const CharT* start,
                                          const CharT* end, int base,
                                          const CharT** endp, double* dp);

/*
 * This is like GetPrefixInteger, but only deals with base 10, and doesn't have
 * and |endp| outparam.  It should only be used when the characters are known to
 * only contain digits.
 */
extern MOZ_MUST_USE bool GetDecimalInteger(JSContext* cx, const char16_t* start,
                                           const char16_t* end, double* dp);

extern MOZ_MUST_USE bool StringToNumber(JSContext* cx, JSString* str,
                                        double* result);

/* ES5 9.3 ToNumber, overwriting *vp with the appropriate number value. */
MOZ_ALWAYS_INLINE MOZ_MUST_USE bool ToNumber(JSContext* cx,
                                             JS::MutableHandleValue vp) {
  if (vp.isNumber()) return true;
  double d;
  extern JS_PUBLIC_API bool ToNumberSlow(JSContext * cx, HandleValue v,
                                         double* dp);
  if (!ToNumberSlow(cx, vp, &d)) return false;

  vp.setNumber(d);
  return true;
}

MOZ_MUST_USE bool num_parseInt(JSContext* cx, unsigned argc, Value* vp);

} /* namespace js */

/*
 * Similar to strtod except that it replaces overflows with infinities of the
 * correct sign, and underflows with zeros of the correct sign.  Guaranteed to
 * return the closest double number to the given input in dp.
 *
 * Also allows inputs of the form [+|-]Infinity, which produce an infinity of
 * the appropriate sign.  The case of the "Infinity" string must match exactly.
 * If the string does not contain a number, set *dEnd to begin and return 0.0
 * in *d.
 *
 * Return false if out of memory.
 */
template <typename CharT>
extern MOZ_MUST_USE bool js_strtod(JSContext* cx, const CharT* begin,
                                   const CharT* end, const CharT** dEnd,
                                   double* d);

namespace js {

extern MOZ_MUST_USE bool num_toString(JSContext* cx, unsigned argc, Value* vp);

extern MOZ_MUST_USE bool num_valueOf(JSContext* cx, unsigned argc, Value* vp);

static MOZ_ALWAYS_INLINE bool ValueFitsInInt32(const Value& v, int32_t* pi) {
  if (v.isInt32()) {
    *pi = v.toInt32();
    return true;
  }
  return v.isDouble() && mozilla::NumberIsInt32(v.toDouble(), pi);
}

/*
 * Returns true if the given value is definitely an index: that is, the value
 * is a number that's an unsigned 32-bit integer.
 *
 * This method prioritizes common-case speed over accuracy in every case.  It
 * can produce false negatives (but not false positives): some values which are
 * indexes will be reported not to be indexes by this method.  Users must
 * consider this possibility when using this method.
 */
static MOZ_ALWAYS_INLINE bool IsDefinitelyIndex(const Value& v,
                                                uint32_t* indexp) {
  if (v.isInt32() && v.toInt32() >= 0) {
    *indexp = v.toInt32();
    return true;
  }

  int32_t i;
  if (v.isDouble() && mozilla::NumberIsInt32(v.toDouble(), &i) && i >= 0) {
    *indexp = uint32_t(i);
    return true;
  }

  if (v.isString() && v.toString()->hasIndexValue()) {
    *indexp = v.toString()->getIndexValue();
    return true;
  }

  return false;
}

/* ES5 9.4 ToInteger. */
static MOZ_MUST_USE inline bool ToInteger(JSContext* cx, HandleValue v,
                                          double* dp) {
  if (v.isInt32()) {
    *dp = v.toInt32();
    return true;
  }
  if (v.isDouble()) {
    *dp = v.toDouble();
  } else if (v.isString() && v.toString()->hasIndexValue()) {
    *dp = v.toString()->getIndexValue();
    return true;
  } else {
    extern JS_PUBLIC_API bool ToNumberSlow(JSContext * cx, HandleValue v,
                                           double* dp);
    if (!ToNumberSlow(cx, v, dp)) return false;
  }
  *dp = JS::ToInteger(*dp);
  return true;
}

/* ES2017 draft 7.1.17 ToIndex
 *
 * Return true and set |*index| to the integer value if |v| is a valid
 * integer index value. Otherwise report a RangeError and return false.
 *
 * The returned index will always be in the range 0 <= *index <= 2^53-1.
 */
MOZ_MUST_USE bool ToIndex(JSContext* cx, JS::HandleValue v,
                          const unsigned errorNumber, uint64_t* index);

static MOZ_MUST_USE inline bool ToIndex(JSContext* cx, JS::HandleValue v,
                                        uint64_t* index) {
  return ToIndex(cx, v, JSMSG_BAD_INDEX, index);
}

MOZ_MUST_USE inline bool SafeAdd(int32_t one, int32_t two, int32_t* res) {
#if BUILTIN_CHECKED_ARITHMETIC_SUPPORTED(__builtin_sadd_overflow)
  // Using compiler's builtin function.
  return !__builtin_sadd_overflow(one, two, res);
#else
  // Use unsigned for the 32-bit operation since signed overflow gets
  // undefined behavior.
  *res = uint32_t(one) + uint32_t(two);
  int64_t ores = (int64_t)one + (int64_t)two;
  return ores == (int64_t)*res;
#endif
}

MOZ_MUST_USE inline bool SafeSub(int32_t one, int32_t two, int32_t* res) {
#if BUILTIN_CHECKED_ARITHMETIC_SUPPORTED(__builtin_ssub_overflow)
  return !__builtin_ssub_overflow(one, two, res);
#else
  *res = uint32_t(one) - uint32_t(two);
  int64_t ores = (int64_t)one - (int64_t)two;
  return ores == (int64_t)*res;
#endif
}

MOZ_MUST_USE inline bool SafeMul(int32_t one, int32_t two, int32_t* res) {
#if BUILTIN_CHECKED_ARITHMETIC_SUPPORTED(__builtin_smul_overflow)
  return !__builtin_smul_overflow(one, two, res);
#else
  *res = uint32_t(one) * uint32_t(two);
  int64_t ores = (int64_t)one * (int64_t)two;
  return ores == (int64_t)*res;
#endif
}

} /* namespace js */

#endif /* jsnum_h */