/src/serenity/AK/Math/Rounding.h

Source
/*
 * Copyright (c) 2021-2026, Leon Albrecht <leon2002.la@gmail.com>.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/Concepts.h>
#include <AK/Math/Division.h>
#include <AK/NumericLimits.h>

#include <AK/Math/Macros.h>

namespace AK {

namespace Rounding {
template<FloatingPoint T>
constexpr T ceil(T num)
{
    // FIXME: SSE4.1 rounds[sd] num, res, 0b110
    if (is_constant_evaluated()) {
        if (num < NumericLimits<i64>::min() || num > NumericLimits<i64>::max())
            return num;
        return (static_cast<T>(static_cast<i64>(num)) == num)
            ? static_cast<i64>(num)
            : static_cast<i64>(num) + ((num > 0) ? 1 : 0);
    }
#if ARCH(AARCH64)
    AARCH64_INSTRUCTION(frintp, num);
#else
    CALL_BUILTIN(ceil, num);
#endif
}

template<FloatingPoint T>
constexpr T floor(T num)
{
    // FIXME: SSE4.1 rounds[sd] num, res, 0b101
    if (is_constant_evaluated()) {
        if (num < NumericLimits<i64>::min() || num > NumericLimits<i64>::max())
            return num;
        return (static_cast<T>(static_cast<i64>(num)) == num)
            ? static_cast<i64>(num)
            : static_cast<i64>(num) - ((num > 0) ? 0 : 1);
    }
#if ARCH(AARCH64)
    AARCH64_INSTRUCTION(frintm, num);
#else
    CALL_BUILTIN(floor, num);
#endif
}

template<FloatingPoint T>
constexpr T trunc(T num)
{
#if ARCH(AARCH64)
    if (is_constant_evaluated()) {
        if (num < NumericLimits<i64>::min() || num > NumericLimits<i64>::max())
            return num;
        return static_cast<T>(static_cast<i64>(num));
    }
    AARCH64_INSTRUCTION(frintz, num);
#endif
    // FIXME: Use dedicated instruction in the non constexpr case
    //        SSE4.1: rounds[sd] %num, %res, 0b111
    if (num < NumericLimits<i64>::min() || num > NumericLimits<i64>::max())
        return num;
    return static_cast<T>(static_cast<i64>(num));
}

template<FloatingPoint T>
constexpr T rint(T x)
{
    CONSTEXPR_STATE(rint, x);
    // Note: This does break tie to even
    //       But the behavior of frndint/rounds[ds]/frintx can be configured
    //       through the floating point control registers.
    // FIXME: We should decide if we rename this to allow us to get away from
    //        the configurability "burden" rint has
    //        this would make us use `rounds[sd] %num, %res, 0b100`
    //        and `frintn` respectively,
    //        no such guaranteed round exists for x87 `frndint`
#if ARCH(X86_64)
#    ifdef __SSE4_1__
    if constexpr (IsSame<T, double>) {
        T r;
        asm(
            "roundsd %1, %0"
            : "=x"(r)
            : "x"(x));
        return r;
    }
    if constexpr (IsSame<T, float>) {
        T r;
        asm(
            "roundss %1, %0"
            : "=x"(r)
            : "x"(x));
        return r;
    }
#    else
    asm(
        "frndint"
        : "+t"(x));
    return x;
#    endif
#elif ARCH(AARCH64)
    AARCH64_INSTRUCTION(frintx, x);
#elif ARCH(RISCV64)
    if (__builtin_isnan(x))
        return x;

    // Floating point values have a gap size of >= 1 for values above 2^mantissa_bits - 1.
    if (fabs(x) > FloatExtractor<T>::mantissa_max)
        return x;

    if constexpr (IsSame<T, float>) {
        i64 r;
        asm("fcvt.l.s %0, %1, dyn"
            : "=r"(r)
            : "f"(x));
        return copysign(static_cast<float>(r), x);
    }
    if constexpr (IsSame<T, double>) {
        i64 r;
        asm("fcvt.l.d %0, %1, dyn"
            : "=r"(r)
            : "f"(x));
        return copysign(static_cast<double>(r), x);
    }
    if constexpr (IsSame<T, long double>)
        TODO_RISCV64();
#endif
    TODO();
}

template<FloatingPoint T>
constexpr T round(T x)
{
    CONSTEXPR_STATE(round, x);
    // Note: This is break-tie-away-from-zero, so not the hw's understanding of
    //       "nearest", which would be towards even.
    if (x == 0.)
        return x;
    if (x > 0.)
        return floor(x + .5);
    return ceil(x - .5);
}

template<Integral I, FloatingPoint P>
ALWAYS_INLINE I round_to(P value);

#if ARCH(X86_64)
template<Integral I>
ALWAYS_INLINE I round_to(long double value)
{
    // Note: fistps outputs into a signed integer location (i16, i32, i64),
    //       so lets be nice and tell the compiler that.
    Conditional<sizeof(I) >= sizeof(i16), MakeSigned<I>, i16> ret;
    if constexpr (sizeof(I) == sizeof(i64)) {
        asm("fistpll %0"
            : "=m"(ret)
            : "t"(value)
            : "st");
    } else if constexpr (sizeof(I) == sizeof(i32)) {
        asm("fistpl %0"
            : "=m"(ret)
            : "t"(value)
            : "st");
    } else {
        asm("fistps %0"
            : "=m"(ret)
            : "t"(value)
            : "st");
    }
    return static_cast<I>(ret);
}

template<Integral I>
ALWAYS_INLINE I round_to(float value)
{
    // FIXME: round_to<u64> might will cause issues, aka the indefinite value being set,
    //        if the value surpasses the i64 limit, even if the result could fit into an u64
    //        To solve this we would either need to detect that value or do a range check and
    //        then do a more specialized conversion, which might include a division (which is expensive)
    if constexpr (sizeof(I) == sizeof(i64) || IsSame<I, u32>) {
        i64 ret;
        asm("cvtss2si %1, %0"
            : "=r"(ret)
            : "xm"(value));
        return static_cast<I>(ret);
    }
    i32 ret;
    asm("cvtss2si %1, %0"
        : "=r"(ret)
        : "xm"(value));
    return static_cast<I>(ret);
}

template<Integral I>
ALWAYS_INLINE I round_to(double value)
{
    // FIXME: round_to<u64> might will cause issues, aka the indefinite value being set,
    //        if the value surpasses the i64 limit, even if the result could fit into an u64
    //        To solve this we would either need to detect that value or do a range check and
    //        then do a more specialized conversion, which might include a division (which is expensive)
    if constexpr (sizeof(I) == sizeof(i64) || IsSame<I, u32>) {
        i64 ret;
        asm("cvtsd2si %1, %0"
            : "=r"(ret)
            : "xm"(value));
        return static_cast<I>(ret);
    }
    i32 ret;
    asm("cvtsd2si %1, %0"
        : "=r"(ret)
        : "xm"(value));
    return static_cast<I>(ret);
}

#elif ARCH(AARCH64)
template<SignedIntegral I>
ALWAYS_INLINE I round_to(float value)
{
    if constexpr (sizeof(I) <= sizeof(u32)) {
        i32 res;
        asm("fcvtns %w0, %s1"
            : "=r"(res)
            : "w"(value));
        return static_cast<I>(res);
    }
    i64 res;
    asm("fcvtns %0, %s1"
        : "=r"(res)
        : "w"(value));
    return static_cast<I>(res);
}

template<SignedIntegral I>
ALWAYS_INLINE I round_to(double value)
{
    if constexpr (sizeof(I) <= sizeof(u32)) {
        i32 res;
        asm("fcvtns %w0, %d1"
            : "=r"(res)
            : "w"(value));
        return static_cast<I>(res);
    }
    i64 res;
    asm("fcvtns %0, %d1"
        : "=r"(res)
        : "w"(value));
    return static_cast<I>(res);
}

template<UnsignedIntegral U>
ALWAYS_INLINE U round_to(float value)
{
    if constexpr (sizeof(U) <= sizeof(u32)) {
        u32 res;
        asm("fcvtnu %w0, %s1"
            : "=r"(res)
            : "w"(value));
        return static_cast<U>(res);
    }
    i64 res;
    asm("fcvtnu %0, %s1"
        : "=r"(res)
        : "w"(value));
    return static_cast<U>(res);
}

template<UnsignedIntegral U>
ALWAYS_INLINE U round_to(double value)
{
    if constexpr (sizeof(U) <= sizeof(u32)) {
        u32 res;
        asm("fcvtns %w0, %d1"
            : "=r"(res)
            : "w"(value));
        return static_cast<U>(res);
    }
    i64 res;
    asm("fcvtns %0, %d1"
        : "=r"(res)
        : "w"(value));
    return static_cast<U>(res);
}

#else
template<Integral I, FloatingPoint P>
ALWAYS_INLINE I round_to(P value)
{
    if constexpr (IsSame<P, long double>)
        return static_cast<I>(__builtin_llrintl(value));
    if constexpr (IsSame<P, double>)
        return static_cast<I>(__builtin_llrint(value));
    if constexpr (IsSame<P, float>)
        return static_cast<I>(__builtin_llrintf(value));
}
#endif

}

using Rounding::ceil;
using Rounding::floor;
using Rounding::rint;
using Rounding::round;
using Rounding::round_to;
using Rounding::trunc;

template<Integral I, typename T>
constexpr I clamp_to(T value)
{
    constexpr auto max = static_cast<T>(NumericLimits<I>::max());
    if constexpr (max > 0) {
        if (value >= static_cast<T>(NumericLimits<I>::max()))
            return NumericLimits<I>::max();
    }

    constexpr auto min = static_cast<T>(NumericLimits<I>::min());
    if constexpr (min <= 0) {
        if (value <= static_cast<T>(NumericLimits<I>::min()))
            return NumericLimits<I>::min();
    }

    if constexpr (IsFloatingPoint<T>)
        return round_to<I>(value);

    return value;
}

// Wrap a to keep it in the range [-b, b].
template<typename T>
constexpr T wrap_to_range(T a, IdentityType<T> b)
{
    return fmod(fmod(a + b, 2 * b) + 2 * b, 2 * b) - b;
}

#include <AK/Math/UndefMacros.h>

}

#if USING_AK_GLOBALLY
using AK::round_to;
#endif

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Created: 2026-10-28 07:05