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Move floating-point math functions into a new lib/math
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Nick Mathewson
@@ -127,100 +127,6 @@ ENABLE_GCC_WARNING(aggregate-return)
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* Math
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* ===== */
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/**
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* Returns the natural logarithm of d base e. We defined this wrapper here so
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* to avoid conflicts with old versions of tor_log(), which were named log().
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*/
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double
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tor_mathlog(double d)
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{
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return log(d);
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}
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/** Return the long integer closest to <b>d</b>. We define this wrapper
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* here so that not all users of math.h need to use the right incantations
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* to get the c99 functions. */
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long
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tor_lround(double d)
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{
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#if defined(HAVE_LROUND)
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return lround(d);
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#elif defined(HAVE_RINT)
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return (long)rint(d);
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#else
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return (long)(d > 0 ? d + 0.5 : ceil(d - 0.5));
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#endif /* defined(HAVE_LROUND) || ... */
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}
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/** Return the 64-bit integer closest to d. We define this wrapper here so
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* that not all users of math.h need to use the right incantations to get the
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* c99 functions. */
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int64_t
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tor_llround(double d)
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{
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#if defined(HAVE_LLROUND)
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return (int64_t)llround(d);
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#elif defined(HAVE_RINT)
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return (int64_t)rint(d);
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#else
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return (int64_t)(d > 0 ? d + 0.5 : ceil(d - 0.5));
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#endif /* defined(HAVE_LLROUND) || ... */
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}
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/** Transform a random value <b>p</b> from the uniform distribution in
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* [0.0, 1.0[ into a Laplace distributed value with location parameter
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* <b>mu</b> and scale parameter <b>b</b>. Truncate the final result
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* to be an integer in [INT64_MIN, INT64_MAX]. */
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int64_t
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sample_laplace_distribution(double mu, double b, double p)
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{
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double result;
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tor_assert(p >= 0.0 && p < 1.0);
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/* This is the "inverse cumulative distribution function" from:
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* http://en.wikipedia.org/wiki/Laplace_distribution */
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if (p <= 0.0) {
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/* Avoid taking log(0.0) == -INFINITY, as some processors or compiler
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* options can cause the program to trap. */
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return INT64_MIN;
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}
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result = mu - b * (p > 0.5 ? 1.0 : -1.0)
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* tor_mathlog(1.0 - 2.0 * fabs(p - 0.5));
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return clamp_double_to_int64(result);
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}
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/** Add random noise between INT64_MIN and INT64_MAX coming from a Laplace
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* distribution with mu = 0 and b = <b>delta_f</b>/<b>epsilon</b> to
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* <b>signal</b> based on the provided <b>random</b> value in [0.0, 1.0[.
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* The epsilon value must be between ]0.0, 1.0]. delta_f must be greater
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* than 0. */
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int64_t
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add_laplace_noise(int64_t signal_, double random_, double delta_f,
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double epsilon)
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{
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int64_t noise;
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/* epsilon MUST be between ]0.0, 1.0] */
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tor_assert(epsilon > 0.0 && epsilon <= 1.0);
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/* delta_f MUST be greater than 0. */
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tor_assert(delta_f > 0.0);
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/* Just add noise, no further signal */
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noise = sample_laplace_distribution(0.0,
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delta_f / epsilon,
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random_);
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/* Clip (signal + noise) to [INT64_MIN, INT64_MAX] */
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if (noise > 0 && INT64_MAX - noise < signal_)
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return INT64_MAX;
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else if (noise < 0 && INT64_MIN - noise > signal_)
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return INT64_MIN;
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else
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return signal_ + noise;
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}
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/* =====
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* String manipulation
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* ===== */
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@@ -389,67 +295,3 @@ load_windows_system_library(const TCHAR *library_name)
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return LoadLibrary(path);
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}
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#endif /* defined(_WIN32) */
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/** Cast a given double value to a int64_t. Return 0 if number is NaN.
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* Returns either INT64_MIN or INT64_MAX if number is outside of the int64_t
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* range. */
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int64_t
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clamp_double_to_int64(double number)
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{
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int exponent;
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#if defined(MINGW_ANY) && GCC_VERSION >= 409
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/*
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Mingw's math.h uses gcc's __builtin_choose_expr() facility to declare
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isnan, isfinite, and signbit. But as implemented in at least some
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versions of gcc, __builtin_choose_expr() can generate type warnings
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even from branches that are not taken. So, suppress those warnings.
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*/
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#define PROBLEMATIC_FLOAT_CONVERSION_WARNING
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DISABLE_GCC_WARNING(float-conversion)
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#endif /* defined(MINGW_ANY) && GCC_VERSION >= 409 */
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/*
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With clang 4.0 we apparently run into "double promotion" warnings here,
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since clang thinks we're promoting a double to a long double.
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*/
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#if defined(__clang__)
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#if __has_warning("-Wdouble-promotion")
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#define PROBLEMATIC_DOUBLE_PROMOTION_WARNING
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DISABLE_GCC_WARNING(double-promotion)
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#endif
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#endif /* defined(__clang__) */
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/* NaN is a special case that can't be used with the logic below. */
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if (isnan(number)) {
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return 0;
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}
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/* Time to validate if result can overflows a int64_t value. Fun with
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* float! Find that exponent exp such that
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* number == x * 2^exp
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* for some x with abs(x) in [0.5, 1.0). Note that this implies that the
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* magnitude of number is strictly less than 2^exp.
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*
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* If number is infinite, the call to frexp is legal but the contents of
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* are exponent unspecified. */
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frexp(number, &exponent);
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/* If the magnitude of number is strictly less than 2^63, the truncated
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* version of number is guaranteed to be representable. The only
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* representable integer for which this is not the case is INT64_MIN, but
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* it is covered by the logic below. */
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if (isfinite(number) && exponent <= 63) {
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return (int64_t)number;
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}
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/* Handle infinities and finite numbers with magnitude >= 2^63. */
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return signbit(number) ? INT64_MIN : INT64_MAX;
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#ifdef PROBLEMATIC_DOUBLE_PROMOTION_WARNING
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ENABLE_GCC_WARNING(double-promotion)
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#endif
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#ifdef PROBLEMATIC_FLOAT_CONVERSION_WARNING
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ENABLE_GCC_WARNING(float-conversion)
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#endif
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}
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@@ -62,13 +62,6 @@ void tor_log_mallinfo(int severity);
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#define bool_neq(a,b) (!(a)!=!(b))
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/* Math functions */
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double tor_mathlog(double d) ATTR_CONST;
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long tor_lround(double d) ATTR_CONST;
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int64_t tor_llround(double d) ATTR_CONST;
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int64_t sample_laplace_distribution(double mu, double b, double p);
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int64_t add_laplace_noise(int64_t signal, double random, double delta_f,
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double epsilon);
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int64_t clamp_double_to_int64(double number);
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/* String manipulation */
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