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Vol. 2A 3-411
INSTRUCTION SET REFERENCE, A-M
FXAM—ExamineModR/M
FXAM—ExamineModR/M
Description
Examines the contents of the ST(0) register and sets the condition code flags C0, C2,
and C3 in the FPU status word to indicate the class of value or number in the register
(see the table below).
.
The C1 flag is set to the sign of the value in ST(0), regardless of whether the register
is empty or full.
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
Operation
C1 ← sign bit of ST; (* 0 for positive, 1 for negative *)
CASE (class of value or number in ST(0)) OF
Unsupported:C3, C2, C0 ← 000;
NaN: C3, C2, C0 ← 001;
Normal: C3, C2, C0 ← 010;
Infinity: C3, C2, C0 ← 011;
Zero: C3, C2, C0 ← 100;
Empty: C3, C2, C0 ← 101;
Denormal: C3, C2, C0 ← 110;
ESAC;
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
D9 E5 FXAM Valid Valid Classify value or number in ST(0).
Table 3-47. FXAM Results
Class C3 C2 C0
Unsupported 0 0 0
NaN 0 0 1
Normal finite number 0 1 0
Infinity 0 1 1
Zero 1 0 0
Empty 1 0 1
Denormal number 1 1 0