Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3, Manual

Page: 1399 / 1898

Volume 4: Base IA-32 Instruction Reference 4:97
F2XM1—Compute 2
x
-1
Description
Calculates the exponential value of 2 to the power of the source operand minus 1. The
source operand is located in register ST(0) and the result is also stored in ST(0). The
value of the source operand must lie in the range -1.0 to +1.0. If the source value is
outside this range, the result is undefined.
The following table shows the results obtained when computing the exponential value
of various classes of numbers, assuming that neither overflow nor underflow occurs:
Values other than 2 can be exponentiated using the following formula:
x
y
= 2
(y

log
2
x)
Operation
ST(0)

(2
ST(0)

1);
FPU Flags Affected
C1 Set to 0 if stack underflow occurred.
Indicates rounding direction if the inexact-result exception (#P) is
generated: 0 = not roundup; 1 = roundup.
C0, C2, C3 Undefined.
Additional Itanium System Environment Exceptions
Itanium Reg Faults Disabled FP Register Fault if PSR.dfl is 1, NaT Register Consumption
Abort.
Floating-point Exceptions
#IS Stack underflow occurred.
#IA Source operand is an SNaN value or unsupported format.
#D Result is a denormal value.
#U Result is too small for destination format.
#P Value cannot be represented exactly in destination format.
Opcode Instruction Description
D9 F0 F2XM1 Replace ST(0) with (2
ST(0)
- 1)
ST(0) SRC ST(0) DEST
-1.0 to

0

0.5 to

0

0

0

0 +0
+0 to +1.0 +0 to 1.0