Intel 253666-024US User Manual
Page 480
3-434 Vol. 2A
FYL2XP1—Compute y * log2(x +1)
INSTRUCTION SET REFERENCE, A-M
equation is used to calculate the scale factor for a particular logarithm base, where n
is the logarithm base desired for the result of the FYL2XP1 instruction:
scale factor ← log
n
2
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
Operation
ST(1) ← ST(1)
∗
log
2
(ST(0) + 1.0);
PopRegisterStack;
FPU Flags Affected
C1
Set to 0 if stack underflow occurred.
Set if result was rounded up; cleared otherwise.
C0, C2, C3
Undefined.
Floating-Point Exceptions
#IS
Stack underflow occurred.
#IA
Either operand is an SNaN value or unsupported format.
#D
Source operand is a denormal value.
#U
Result is too small for destination format.
#O
Result is too large for destination format.
#P
Value cannot be represented exactly in destination format.
Protected Mode Exceptions
#NM
CR0.EM[bit 2] or CR0.TS[bit 3] = 1.
#MF
If there is a pending x87 FPU exception.
#UD
If the LOCK prefix is used.
Real-Address Mode Exceptions
Same exceptions as in protected mode.
Virtual-8086 Mode Exceptions
Same exceptions as in protected mode.
Compatibility Mode Exceptions
Same exceptions as in protected mode.
64-Bit Mode Exceptions
Same exceptions as in protected mode.