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3-146 Vol. 2A CMPSS—Compare Scalar Single-Precision Floating-Point Values
INSTRUCTION SET REFERENCE, A-M
CMPSS—Compare Scalar Single-Precision Floating-Point Values
Description
Compares the low single-precision floating-point values in the source operand
(second operand) and the destination operand (first operand) and returns the results
of the comparison to the destination operand. The comparison predicate operand
(third operand) specifies the type of comparison performed. The comparison result is
a doubleword mask of all 1s (comparison true) or all 0s (comparison false).
The source operand can be an XMM register or a 32-bit memory location. The desti-
nation operand is an XMM register. The result is stored in the low doubleword of the
destination operand; the 3 high-order doublewords remain unchanged. The compar-
ison predicate operand is an 8-bit immediate, the first 3 bits of which define the type
of comparison to be made (see Table 3-7). Bits 4 through 7 of the immediate are
reserved.
The unordered relationship is true when at least one of the two source operands
being compared is a NaN; the ordered relationship is true when neither source
operand is a NaN
A subsequent computational instruction that uses the mask result in the destination
operand as an input operand will not generate a fault, since a mask of all 0s corre-
sponds to a floating-point value of +0.0 and a mask of all 1s corresponds to a QNaN.
Some of the comparisons listed in Table 3-7 can be achieved only through software
emulation. For these comparisons the program must swap the operands (copying
registers when necessary to protect the data that will now be in the destination
operand), and then perform the compare using a different predicate. The predicate
to be used for these emulations is listed in Table 3-7 under the heading Emulation.
Compilers and assemblers may implement the following two-operand pseudo-ops in
addition to the three-operand CMPSS instruction. See Table 3-11.
Opcode Instruction 64-Bit Mode Compat/
Leg Mode
Description
F3 0F C2 /r ib CMPSS xmm1,
xmm2/m32,
imm8
Valid Valid Compare low single-precision
floating-point value in
xmm2/m32 and xmm1 using
imm8 as comparison
predicate.