jcs.org / qemu
qemu with hax to log dma reads & writes jcs.org/2018/11/12/vfio
fork atom

softfloat,m68k: disable floatx80_invalid_encoding() for m68k

According to the comment, this definition of invalid encoding is given
by intel developer's manual, and doesn't comply with 680x0 FPU.

With m68k, the explicit integer bit can be zero in the case of:
- zeros (exp == 0, mantissa == 0)
- denormalized numbers (exp == 0, mantissa != 0)
- unnormalized numbers (exp != 0, exp < 0x7FFF)
- infinities (exp == 0x7FFF, mantissa == 0)
- not-a-numbers (exp == 0x7FFF, mantissa != 0)

For infinities and NaNs, the explicit integer bit can be either one or
zero.

The IEEE 754 standard does not define a zero integer bit. Such a number
is an unnormalized number. Hardware does not directly support
denormalized and unnormalized numbers, but implicitly supports them by
trapping them as unimplemented data types, allowing efficient conversion
in software.

See "M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL",
"1.6 FLOATING-POINT DATA TYPES"

We will implement in the m68k TCG emulator the FP_UNIMP exception to
trap into the kernel to normalize the number. In case of linux-user,
the number will be normalized by QEMU.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200612140400.2130118-1-laurent@vivier.eu>

Laurent Vivier d159dd05 852002b5

+24
+24
include/fpu/softfloat.h
··· 794 794 *----------------------------------------------------------------------------*/ 795 795 static inline bool floatx80_invalid_encoding(floatx80 a) 796 796 { 797 + #if defined(TARGET_M68K) 798 + /*------------------------------------------------------------------------- 799 + | With m68k, the explicit integer bit can be zero in the case of: 800 + | - zeros (exp == 0, mantissa == 0) 801 + | - denormalized numbers (exp == 0, mantissa != 0) 802 + | - unnormalized numbers (exp != 0, exp < 0x7FFF) 803 + | - infinities (exp == 0x7FFF, mantissa == 0) 804 + | - not-a-numbers (exp == 0x7FFF, mantissa != 0) 805 + | 806 + | For infinities and NaNs, the explicit integer bit can be either one or 807 + | zero. 808 + | 809 + | The IEEE 754 standard does not define a zero integer bit. Such a number 810 + | is an unnormalized number. Hardware does not directly support 811 + | denormalized and unnormalized numbers, but implicitly supports them by 812 + | trapping them as unimplemented data types, allowing efficient conversion 813 + | in software. 814 + | 815 + | See "M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL", 816 + | "1.6 FLOATING-POINT DATA TYPES" 817 + *------------------------------------------------------------------------*/ 818 + return false; 819 + #else 797 820 return (a.low & (1ULL << 63)) == 0 && (a.high & 0x7FFF) != 0; 821 + #endif 798 822 } 799 823 800 824 #define floatx80_zero make_floatx80(0x0000, 0x0000000000000000LL)