
Chapter 4: 128-Bit Media and Scientific Programming
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AMD 64-Bit Technology
denormals are zeros (DAZ) bit, the processor does not set the
DE bit. (See “Denormalized (Tiny) Numbers” on page 154.)
Zero-Divide Exception (ZE).
Bit 2. The processor sets this bit to 1
when a non-zero number is divided by zero.
Overflow Exception (OE).
Bit 3. The processor sets this bit to 1 when
the absolute value of a rounded result is larger than the largest
representable normalized floating-point number for the
destination format. (See “Normalized Numbers” on page 153.)
Underflow Exception (UE).
Bit 4. The processor sets this bit to 1
when the absolute value of a rounded non-zero result is too
small to be represented as a normalized floating-point number
for the destination format. (See “Normalized Numbers” on
page 153.)
The underflow exception has an unusual behavior. When
masked by the UM bit (bit 11), the processor only reports a UE
exception if the UE occurs
together with
a precision exception
(PE). Also, see bit 15, the flush-to-zero (FZ) bit.
Precision Exception (PE).
Bit 5. The processor sets this bit to 1 when
a floating-point result, after rounding, differs from the
infinitely precise result and thus cannot be represented exactly
in the specified destination format. The PE exception is also
called the
inexact-result
exception.
Denormals Are Zeros (DAZ).
Bit 6. Software can set this bit to 1 to
enable the DAZ mode, if the hardware implementation
supports this mode. In the DAZ mode, when the processor
encounters source operands in the denormalized format it
converts them to signed zero values, with the sign of the
denormalized source operand, before operating on them, and
the processor does not set the denormalized-operand exception
(DE) bit, regardless of whether such exceptions are masked or
unmasked.
Support for the DAZ bit is indicated by the MXCSR Mask field
in the FXSAVE memory image, as described in “Saving Media
and x87 Processor State” in Volume 2. The DAZ mode does not
comply with the
IEEE Standard for Binary Floating-Point
Arithmetic
(ANSI/IEEE Std 754).
Exception Masks (PM, UM, OM, ZM, DM, IM).
Bits 12–7. Software can
set these bits to mask, or clear this bits to unmask, the