libc/fuzzing/stdlib/strtofloat_fuzz.cpp

//===-- strtofloat_fuzz.cpp -----------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// Fuzzing test for llvm-libc atof implementation.
///
//===----------------------------------------------------------------------===//
#include "src/stdlib/atof.h"
#include "src/stdlib/strtod.h"
#include "src/stdlib/strtof.h"
#include "src/stdlib/strtold.h"

#include "src/__support/FPUtil/FPBits.h"

#include "hdr/math_macros.h"
#include <stddef.h>
#include <stdint.h>

#include "utils/MPFRWrapper/mpfr_inc.h"

using LIBC_NAMESPACE::fputil::FPBits;

// This function calculates the effective precision for a given float type and
// exponent. Subnormals have a lower effective precision since they don't
// necessarily use all of the bits of the mantissa.
template <typename F> inline constexpr int effective_precision(int exponent) {
  const int full_precision = FPBits<F>::FRACTION_LEN + 1;

  // This is intended to be 0 when the exponent is the lowest normal and
  // increase as the exponent's magnitude increases.
  const int bits_below_normal = (-exponent) - (FPBits<F>::EXP_BIAS - 1);

  // The precision should be the normal, full precision, minus the bits lost
  // by this being a subnormal, minus one for the implicit leading one.
  const int bits_if_subnormal = full_precision - bits_below_normal - 1;

  if (bits_below_normal >= 0) {
    return bits_if_subnormal;
  }
  return full_precision;
}

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
  // const char newstr[] = "123";
  // data = reinterpret_cast<const uint8_t *>(newstr);
  // size = sizeof(newstr);
  uint8_t *container = new uint8_t[size + 1];
  if (!container)
    __builtin_trap();
  size_t i;

  for (i = 0; i < size; ++i) {
    // MPFR's strtofr uses "@" as a base-independent exponent symbol
    if (data[i] != '@')
      container[i] = data[i];
    else {
      container[i] = '#';
    }
  }
  container[size] = '\0'; // Add null terminator to container.

  const char *str_ptr = reinterpret_cast<const char *>(container);

  char *out_ptr = nullptr;

  size_t base = 0;

  // This is just used to determine the base and precision.
  mpfr_t result;
  mpfr_init2(result, 256);
  mpfr_t bin_result;
  mpfr_init2(bin_result, 256);
  mpfr_strtofr(result, str_ptr, &out_ptr, 0 /* base */, MPFR_RNDN);
  ptrdiff_t result_strlen = out_ptr - str_ptr;
  mpfr_strtofr(bin_result, str_ptr, &out_ptr, 2 /* base */, MPFR_RNDN);
  ptrdiff_t bin_result_strlen = out_ptr - str_ptr;

  long double bin_result_ld = mpfr_get_ld(bin_result, MPFR_RNDN);
  long double result_ld = mpfr_get_ld(result, MPFR_RNDN);

  // This detects if mpfr's strtofr selected a base of 2, which libc does not
  // support. If a base 2 decoding is detected, it is replaced by a base 10
  // decoding.
  if ((bin_result_ld != 0.0 || bin_result_strlen == result_strlen) &&
      bin_result_ld == result_ld) {
    mpfr_strtofr(result, str_ptr, &out_ptr, 10 /* base */, MPFR_RNDN);
    result_strlen = out_ptr - str_ptr;
    base = 10;
  }

  auto result_exp = mpfr_get_exp(result);

  mpfr_clear(result);
  mpfr_clear(bin_result);

  // These must be calculated with the correct precision, and not any more, to
  // prevent numbers like 66336650.00...01 (many zeroes) from causing an issue.
  // 66336650 is exactly between two float values (66336652 and 66336648) so the
  // correct float result for 66336650.00...01 is rounding up to 66336652. The
  // correct double is instead 66336650, which when converted to float is
  // rounded down to 66336648. This means we have to compare against the correct
  // precision to get the correct result.

  // TODO: Add support for other rounding modes.
  int float_precision = effective_precision<float>(result_exp);
  if (float_precision >= 2) {
    mpfr_t mpfr_float;
    mpfr_init2(mpfr_float, float_precision);
    mpfr_strtofr(mpfr_float, str_ptr, &out_ptr, base, MPFR_RNDN);
    float volatile float_result = mpfr_get_flt(mpfr_float, MPFR_RNDN);
    auto volatile strtof_result = LIBC_NAMESPACE::strtof(str_ptr, &out_ptr);
    ptrdiff_t strtof_strlen = out_ptr - str_ptr;
    if (result_strlen != strtof_strlen)
      __builtin_trap();
    // If any result is NaN, all of them should be NaN. We can't use the usual
    // comparisons because NaN != NaN.
    if (FPBits<float>(float_result).is_nan() !=
        FPBits<float>(strtof_result).is_nan())
      __builtin_trap();
    if (!FPBits<float>(float_result).is_nan() && float_result != strtof_result)
      __builtin_trap();
    mpfr_clear(mpfr_float);
  }

  int double_precision = effective_precision<double>(result_exp);
  if (double_precision >= 2) {
    mpfr_t mpfr_double;
    mpfr_init2(mpfr_double, double_precision);
    mpfr_strtofr(mpfr_double, str_ptr, &out_ptr, base, MPFR_RNDN);
    double volatile double_result = mpfr_get_d(mpfr_double, MPFR_RNDN);
    auto volatile strtod_result = LIBC_NAMESPACE::strtod(str_ptr, &out_ptr);
    auto volatile atof_result = LIBC_NAMESPACE::atof(str_ptr);
    ptrdiff_t strtod_strlen = out_ptr - str_ptr;
    if (result_strlen != strtod_strlen)
      __builtin_trap();
    if (FPBits<double>(double_result).is_nan() !=
            FPBits<double>(strtod_result).is_nan() ||
        FPBits<double>(double_result).is_nan() !=
            FPBits<double>(atof_result).is_nan())
      __builtin_trap();
    if (!FPBits<double>(double_result).is_nan() &&
        (double_result != strtod_result || double_result != atof_result))
      __builtin_trap();
    mpfr_clear(mpfr_double);
  }

  int long_double_precision = effective_precision<long double>(result_exp);
  if (long_double_precision >= 2) {
    mpfr_t mpfr_long_double;
    mpfr_init2(mpfr_long_double, long_double_precision);
    mpfr_strtofr(mpfr_long_double, str_ptr, &out_ptr, base, MPFR_RNDN);
    long double volatile long_double_result =
        mpfr_get_ld(mpfr_long_double, MPFR_RNDN);
    auto volatile strtold_result = LIBC_NAMESPACE::strtold(str_ptr, &out_ptr);
    ptrdiff_t strtold_strlen = out_ptr - str_ptr;
    if (result_strlen != strtold_strlen)
      __builtin_trap();
    if (FPBits<long double>(long_double_result).is_nan() ^
        FPBits<long double>(strtold_result).is_nan())
      __builtin_trap();
    if (!FPBits<long double>(long_double_result).is_nan() &&
        long_double_result != strtold_result)
      __builtin_trap();
    mpfr_clear(mpfr_long_double);
  }

  delete[] container;
  return 0;
}