fpusettings.h

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/*
    streflop: STandalone REproducible FLOating-Point
    Nicolas Brodu, 2006
    Code released according to the GNU Lesser General Public License

    Heavily relies on GNU Libm, itself depending on netlib fplibm, GNU MP, and IBM MP lib.
    Uses SoftFloat too.

    Please read the history and copyright information in the documentation provided with the source code
*/

/*
	For reference, the layout of the MXCSR register:
	FZ:RC:RC:PM:UM:OM:ZM:DM:IM:Rsvd:PE:UE:OE:ZE:DE:IE
	15 14 13 12 11 10  9  8  7   6   5  4  3  2  1  0

	And the layout of the 387 FPU control word register:
	Rsvd:Rsvd:Rsvd:X:RC:RC:PC:PC:Rsvd:Rsvd:PM:UM:OM:ZM:DM:IM
	 15   14   13 12 11 10  9  8   7    6   5  4  3  2  1  0

	Where:
		Rsvd - Reserved
		FZ   - Flush to Zero
		RC   - Rounding Control
		PM   - Precision Mask
		UM   - Underflow Mask
		OM   - Overflow Mask
		ZM   - Zerodivide Mask
		DM   - Denormal Mask
		IM   - Invalid Mask
		PE   - Precision Exception
		UE   - Underflow Exception
		OE   - Overflow Exception
		ZE   - Zerodivide Exception
		DE   - Denormal Exception
		IE   - Invalid Exception
		X    - Infinity control (unused on 387 and higher)
		PC   - Precision Control

	Source: Intel Architecture Software Development Manual, Volume 1, Basic Architecture
*/

// Included by the main streflop include file
// module broken apart for logical code separation
#ifndef STREFLOP_FPU_H
#define STREFLOP_FPU_H

// Can safely make the symbols from softfloat visible to user program, protected in namespace
#if defined(STREFLOP_SOFT)
#include "softfloat/softfloat.h"
#endif

namespace streflop {

// We do not use libm, so let's copy a few flags and C99 functions
// Give warning in case these flags would be defined already, this is indication
// of potential confusion!

#if defined(FE_INVALID) || defined(FE_DENORMAL) || defined(FE_DIVBYZERO) || defined(FE_OVERFLOW) || defined(FE_UNDERFLOW) || defined(FE_INEXACT) || defined(FE_DOWNWARD) || defined(FE_TONEAREST) || defined(FE_TOWARDZERO) || defined(FE_UPWARD)

#warning STREFLOP: FE_XXX flags were already defined and will be redefined! Check you do not use the system libm.
#undef FE_INVALID
#undef FE_DENORMAL
#undef FE_DIVBYZERO
#undef FE_OVERFLOW
#undef FE_UNDERFLOW
#undef FE_INEXACT
#undef FE_INEXACT
#undef FE_ALL_EXCEPT
#undef FE_DOWNWARD
#undef FE_TONEAREST
#undef FE_TOWARDZERO
#undef FE_UPWARD
#endif


// Flags for FPU exceptions
enum FPU_Exceptions {

    // Invalid operation. If not signaling, gives NaN instead
    FE_INVALID = 0x0001,
    #define FE_INVALID FE_INVALID

    // Extension: for x86 and SSE
    // Denormal operand. If not signaling, use denormal arithmetic as usual
    FE_DENORMAL = 0x0002,
    #define FE_DENORMAL FE_DENORMAL

    // Division by zero. If not signaling, uses +/- infinity
    FE_DIVBYZERO = 0x0004,
    #define FE_DIVBYZERO FE_DIVBYZERO

    // Overflow. If not signaling, round to nearest (including infinity) according to rounding mode
    FE_OVERFLOW = 0x0008,
    #define FE_OVERFLOW FE_OVERFLOW

    // Underflow. If not signaling, use 0 instead
    FE_UNDERFLOW = 0x0010,
    #define FE_UNDERFLOW FE_UNDERFLOW

    // Rounding was not exact (ex: sqrt(2) is never exact) or when overflow causes rounding
    FE_INEXACT = 0x0020,
    #define FE_INEXACT FE_INEXACT

    // Combination of all the above
    FE_ALL_EXCEPT  = 0x003F
    #define FE_ALL_EXCEPT FE_ALL_EXCEPT
};

// Flags for FPU rounding modes
enum FPU_RoundMode {
    FE_TONEAREST  = 0x0000,
    #define FE_TONEAREST FE_TONEAREST

    FE_DOWNWARD   = 0x0400,
    #define FE_DOWNWARD FE_DOWNWARD

    FE_UPWARD     = 0x0800,
    #define FE_UPWARD FE_UPWARD

    FE_TOWARDZERO = 0x0C00
    #define FE_TOWARDZERO FE_TOWARDZERO
};

/* Note: SSE control word, bits 0..15
0->5: Run-time status flags
6: DAZ (denormals are zero, i.e. don't use denormals if bit is 1)
7->12: Exception flags, same meaning as for the x87 ones
13,14: Rounding flags, same meaning as for the x87 ones
15: Flush to zero (FTZ) for automatic handling of underflow (default is NO)
*/

// plan for portability
#ifdef _MSC_VER
#define STREFLOP_FSTCW(cw) do { short tmp; __asm { fstcw tmp }; (cw) = tmp; } while (0)
#define STREFLOP_FLDCW(cw) do { short tmp = (cw); __asm { fclex }; __asm { fldcw tmp }; } while (0)
#define STREFLOP_STMXCSR(cw) do { int tmp; __asm { stmxcsr tmp }; (cw) = tmp; } while (0)
#define STREFLOP_LDMXCSR(cw) do { int tmp = (cw); __asm { ldmxcsr tmp }; } while (0)
#else
#define STREFLOP_FSTCW(cw) do { asm volatile ("fstcw %0" : "=m" (cw) : ); } while (0)
#define STREFLOP_FLDCW(cw) do { asm volatile ("fclex \n fldcw %0" : : "m" (cw)); } while (0)
#define STREFLOP_STMXCSR(cw) do { asm volatile ("stmxcsr %0" : "=m" (cw) : ); } while (0)
#define STREFLOP_LDMXCSR(cw) do { asm volatile ("ldmxcsr %0" : : "m" (cw) ); } while (0)
#endif

// Subset of all C99 functions

#if defined(STREFLOP_X87)

/// Raise exception for these flags
inline int feraiseexcept(FPU_Exceptions excepts) {
    unsigned short fpu_mode;
    STREFLOP_FSTCW(fpu_mode);
    fpu_mode &= ~( excepts ); // generate error for selection
    STREFLOP_FLDCW(fpu_mode);
    return 0;
}

/// Clear exceptions for these flags
inline int feclearexcept(int excepts) {
    unsigned short fpu_mode;
    STREFLOP_FSTCW(fpu_mode);
    fpu_mode |= excepts;
    STREFLOP_FLDCW(fpu_mode);
    return 0;
}

/// Get current rounding mode
inline int fegetround() {
    unsigned short fpu_mode;
    STREFLOP_FSTCW(fpu_mode);
    return fpu_mode & 0x0C00;
}

/// Set a new rounding mode
inline int fesetround(FPU_RoundMode roundMode) {
    unsigned short fpu_mode;
    STREFLOP_FSTCW(fpu_mode);
    fpu_mode &= 0xF3FF; // clear current mode
    fpu_mode |= roundMode; // sets new mode
    STREFLOP_FLDCW(fpu_mode);
    return 0;
}

typedef short int fenv_t;

/// Default env. Defined in Math.cpp to be 0, and initalized on first use to the permanent holder
extern fenv_t FE_DFL_ENV;

/// Get FP env into the given structure
inline int fegetenv(fenv_t *envp) {
    // check that default env exists, otherwise save it now
    if (!FE_DFL_ENV) STREFLOP_FSTCW(FE_DFL_ENV);
    // Now store env into argument
    STREFLOP_FSTCW(*envp);
    return 0;
}

/// Sets FP env from the given structure
inline int fesetenv(const fenv_t *envp) {
    // check that default env exists, otherwise save it now
    if (!FE_DFL_ENV) STREFLOP_FSTCW(FE_DFL_ENV);
    // Now overwrite current env by argument
    STREFLOP_FLDCW(*envp);
    return 0;
}

/// get env and clear exceptions
inline int feholdexcept(fenv_t *envp) {
    fegetenv(envp);
    feclearexcept(FE_ALL_EXCEPT);
    return 0;
}


template<typename T> inline void streflop_init() {
    struct X {};
    X Unknown_numeric_type;
    // unknown types do not compile
    T error = Unknown_numeric_type;
}

/// Initialize the FPU for the different types
/// this may also be called to switch between code sections using
/// different precisions
template<> inline void streflop_init<Simple>() {
    unsigned short fpu_mode;
    STREFLOP_FSTCW(fpu_mode);
    fpu_mode &= 0xFCFF; // 32 bits internal operations
    STREFLOP_FLDCW(fpu_mode);
}

template<> inline void streflop_init<Double>() {
    unsigned short fpu_mode;
    STREFLOP_FSTCW(fpu_mode);
    fpu_mode &= 0xFCFF;
    fpu_mode |= 0x0200; // 64 bits internal operations
    STREFLOP_FLDCW(fpu_mode);
}

#ifdef Extended
template<> inline void streflop_init<Extended>() {
    unsigned short fpu_mode;
    STREFLOP_FSTCW(fpu_mode);
    fpu_mode &= 0xFCFF;
    fpu_mode |= 0x0300; // 80 bits internal operations
    STREFLOP_FLDCW(fpu_mode);
}
#endif

#elif defined(STREFLOP_SSE)

/// Raise exception for these flags
inline int feraiseexcept(FPU_Exceptions excepts) {
    // Just in case the compiler would store a value on the st(x) registers
    unsigned short x87_mode;
    STREFLOP_FSTCW(x87_mode);
    x87_mode &= ~( excepts ); // generate error for selection
    STREFLOP_FLDCW(x87_mode);

    int sse_mode;