Instructions of change of rounding modes (IEEE754)

Notations

Near is rounding to the nearest,

Down rounding to the minus infinity,

Up rounding to the plus infinity,

and

Chop chopping rounding mode.

LINUX，FreeBSD 3.x　gcc

Define the following global variables:

int   _RoundNear   =0x133a;

int   _RoundDown   =0x173a;

int   _RoundUp     =0x1b3a;

int   _RoundChop   =0x1f3a;

Then, change of rounding mode can be done by

Near	asm volatile (“fldcw _RoundNear”)
Down	asm volatile (“fldcw _RoundDown”)
Up	asm volatile (“fldcw _RoundUp”)
Chop	asm volatile (“fldcw _RoundChop”)

Example of implementation:

On the top of programs, declare the following:

#define Near()   asm volatile (“fldcw _RoundNear”)

#define Down()   asm volatile (“fldcw _RoundDown”)

#define Up()     asm volatile (“fldcw _RoundUp”)

#define Chop()   asm volatile (“fldcw _RoundChop”)

Then, we can change rounding mode by

Near();

Down();

Up();

Chop();

SUN Sparc gcc

Define the following global variables:

int   _RoundNear   =0x00000000L;

int   _RoundDown   =0xc0000000L;

int   _RoundUp     =0x80000000L;

int   _RoundChop   =0x40000000L;

Then, we can change rounding mode by

Near	asm volatile (“ld %0,%%fsr”: :”g” (_RoundNear))
Down	asm volatile (“ld %0,%%fsr”: :”g” (_RoundDown))
Up	asm volatile (“ld %0,%%fsr”: :”g” (_RoundUp))
Chop	asm volatile (“ld %0,%%fsr”: :”g” (_RoundChop))

Window98　GNU-WIN32

Define the following global variables:

int   _RoundNear   =0x133a;

int   _RoundDown   =0x173a;

int   _RoundUp     =0x1b3a;

int   _RoundChop   =0x1f3a;

Then, we can change rounding mode by

Near	asm volatile (“fldcw __RoundNear”)
Down	asm volatile (“fldcw __RoundDown”)
Up	asm volatile (“fldcw __RoundUp”)
Chop	asm volatile (“fldcw __RoundChop”)

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last modified 2001/1/13

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