mxfp.hh

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#ifndef __ARCH_AMDGPU_COMMON_DTYPE_MXFP_HH__
#define __ARCH_AMDGPU_COMMON_DTYPE_MXFP_HH__
 
#include <cmath>
#include <cstdint>
#include <iostream>
 
#include "arch/amdgpu/common/dtype/mxfp_convert.hh"
 
namespace gem5
{
 
namespace AMDGPU
{
 
// Base class for all microscaling types. The sizes of everything are
// determined by the enum fields in the FMT struct. All of these share the
// same operator overloads which convert to float before arithmetic and
// convert back if assigned to a microscaling type.
template<typename FMT>
class mxfp
{
  public:
    mxfp() = default;
    mxfp(float f) : mode(roundTiesToEven)
    {
        data = float_to_mxfp(f);
    }
 
    // Set raw bits, used by gem5 to set a raw value read from VGPRs.
    mxfp(const uint32_t& raw)
    {
        // The info unions end up being "left" aligned. For example, in FP4
        // only the bits 31:28 are used. Shift the input by the storage size
        // of 32 by the type size (sign + exponent + mantissa bits).
        data = raw;
        data <<= (32 - int(FMT::sbits) - int(FMT::ebits) - int(FMT::mbits));
    }
 
    mxfp(const mxfp& f)
    {
        FMT conv_out;
        conv_out = convertMXFP<FMT, decltype(f.getFmt())>(f.getFmt());
        data = conv_out.storage;
    }
 
    mxfp&
    operator=(const float& f)
    {
       data = float_to_mxfp(f);
       return *this;
    }
 
    mxfp&
    operator=(const mxfp& f)
    {
        FMT conv_out;
        conv_out = convertMXFP<FMT, decltype(f.getFmt())>(f.getFmt());
        data = conv_out.storage;
        return *this;
    }
 
    operator float() const
    {
        binary32 out;
        FMT in;
        in.storage = data;
        out = convertMXFP<binary32, FMT>(in, mode);
 
        return out.fp32;
    }
 
    constexpr static int
    size()
    {
        return int(FMT::mbits) + int(FMT::ebits) + int(FMT::sbits);
    }
 
    // Intentionally use storage > size() so that a storage type is not needed
    // as a template parameter.
    uint32_t data = 0;
 
    FMT
    getFmt() const
    {
        FMT out;
        out.storage = data;
        return out;
    }
 
    void
    setFmt(FMT in)
    {
        data = in.storage;
    }
 
    // Used for upcasting
    void
    scaleMul(const float& f)
    {
        binary32 bfp;
        bfp.fp32 = f;
        int scale_val = bfp.exp;
 
        // Scale value of 0xFF is NaN. Scaling by NaN returns NaN.
        // In this implementation, types without NaN define it as max().
        if (scale_val == 0xFF) {
            data = FMT::nan;
            return;
        }
 
        scale_val -= bfp.bias;
 
        FMT in = getFmt();
        int exp = in.exp;
 
        // Our value is zero, scaling by anything remains zero.
        if (exp == 0 && in.mant == 0) {
            return;
        }
 
        if (exp + scale_val > max_exp<FMT>()) {
            in.exp = max_exp<FMT>();
        } else if (exp + scale_val < min_exp<FMT>()) {
            in.exp = min_exp<FMT>();
        } else {
            in.exp = exp + scale_val;
        }
 
        data = in.storage;
    }
 
    // Used for downcasting
    void
    scaleDiv(const float& f)
    {
        binary32 bfp;
        bfp.fp32 = f;
        int scale_val = bfp.exp;
 
        // Scale value of 0xFF is NaN. Scaling by NaN returns NaN.
        // In this implementation, types without NaN define it as max().
        if (scale_val == 0xFF) {
            data = FMT::nan;
            return;
        }
 
        scale_val -= bfp.bias;
 
        FMT in = getFmt();
        int exp = in.exp;
 
        // Our value is zero, scaling by anything remains zero.
        if (exp == 0 && in.mant == 0) {
            return;
        }
 
        if (exp - scale_val > max_exp<FMT>()) {
            in.exp = max_exp<FMT>();
        } else if (exp - scale_val < min_exp<FMT>()) {
            in.exp = min_exp<FMT>();
        } else {
            in.exp = exp - scale_val;
 
            // Output become denorm
            if (in.exp == 0) {
                uint32_t m = in.mant | 1 << FMT::mbits;
                m >>= 1;
                in.mant = m & mask(FMT::mbits);
            }
        }
 
        data = in.storage;
    }
 
    // Helper method specific to AMDGPU instructions.
    void
    omodModifier(unsigned omod)
    {
        // When the VOP3 form is used, instructions with a floating-point
        // result can apply an output modifier (OMOD field) that multiplies
        // the result by: 0.5, 1.0, 2.0 or 4.0
        //
        // 2-bit field in encoding:
        //   0:  Do nothing
        //   1:  Multiply by 2
        //   2:  Multiply by 4
        //   3:  Divide by 2 (multiply by 1/2)
        assert(omod < 4);
 
        if (omod == 1) scaleMul(2.0f);
        if (omod == 2) scaleMul(4.0f);
        if (omod == 3) scaleDiv(2.0f);
    }
 
    void
    clamp(bool do_clamp)
    {
        if (do_clamp) {
            if (*this > 1.0f) {
                *this = 1.0f;
            } else if (*this < 0.0f) {
                *this = 0.0f;
            }
        }
    }
 
    void
    fabs()
    {
        data &= 0x7fffffff;
    }
 
    void
    neg()
    {
        data ^= 0x80000000;
    }
 
  private:
    mxfpRoundingMode mode = roundTiesToEven;
 
    uint32_t
    float_to_mxfp(float f)
    {
        binary32 in;
        in.fp32 = f;
 
        FMT out;
        out.storage = 0;
 
        out = convertMXFP<FMT, binary32>(in, mode);
 
        return out.storage;
    }
};
 
// Unary operators
template<typename T>
inline T operator+(T a)
{
    return a;
}
 
template<typename T>
inline T operator-(T a)
{
    // Flip sign bit
    a.data ^= 0x80000000;
    return a;
}
 
template<typename T>
inline T operator++(T a)
{
    a = a + T(1.0f);
    return a;
}
 
template<typename T>
inline T operator--(T a)
{
    a = a - T(1.0f);
    return a;
}
 
template<typename T>
inline T operator++(T a, int)
{
    T original = a;
    ++a;
    return original;
}
 
template<typename T>
inline T operator--(T a, int)
{
    T original = a;
    --a;
    return original;
}
 
// Math operators
template<typename T>
inline T operator+(T a, T b)
{
    return T(float(a) + float(b));
}
 
template<typename T>
inline T operator-(T a, T b)
{
    return T(float(a) - float(b));
}
 
template<typename T>
inline T operator*(T a, T b)
{
    return T(float(a) * float(b));
}
 
template<typename T>
inline T operator/(T a, T b)
{
    return T(float(a) / float(b));
}
 
template<typename T>
inline T operator+=(T &a, T b)
{
    a = a + b;
    return a;
}
 
template<typename T>
inline T operator-=(T &a, T b)
{
    a = a - b;
    return a;
}
 
template<typename T>
inline T operator*=(T &a, T b)
{
    a = a * b;
    return a;
}
 
template<typename T>
inline T operator/=(T &a, T b)
{
    a = a / b;
    return a;
}
 
// Comparison operators
template<typename T>
inline bool operator<(T a, T b)
{
    return float(a) < float(b);
}
 
template<typename T>
inline bool operator>(T a, T b)
{
    return float(a) > float(b);
}
 
template<typename T>
inline bool operator<=(T a, T b)
{
    return float(a) <= float(b);
}
 
template<typename T>
inline bool operator>=(T a, T b)
{
    return float(a) >= float(b);
}
 
template<typename T>
inline bool operator==(T a, T b)
{
    return float(a) == float(b);
}
 
template<typename T>
inline bool operator!=(T a, T b)
{
    return float(a) != float(b);
}
 
} // namespace AMDGPU
 
} // namespace gem5
 
#endif // __ARCH_AMDGPU_COMMON_DTYPE_MXFP_HH__