Calculate 2^{x} - 1
Hex | Mnemonic | Encoding | Long Mode | Legacy Mode | Description |
---|---|---|---|---|---|
D9 F0 | F2XM1 | None | Valid | Valid | Replace ST(0) with (2ST(0) – 1). |
Computes 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.
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 |
Values other than 2 can be exponentiated using the following formula:
x ^{y} = 2 ^{(y * log 2 x)}
This instruction's operation is the same in non-64-bit modes and 64-bit mode.
ST(0) = (pow(2, ST(0)) - 1);
C1: Set to 0 if stack underflow occurred. Set if result was rounded up; cleared otherwise. C0, C2, C3 are undefined.
Exception | Description |
---|---|
#P | Value cannot be represented exactly in destination format. |
#U | Result is too small for destination format. |
#D | Source is a denormal value. |
#IA | Source operand is an SNaN value or unsupported format. |
#IS | Stack underflow occurred. |
Same exceptions as in protected mode.
Same exceptions as in protected mode.
Same exceptions as in protected mode.
Same exceptions as in protected mode.
Exception | Description |
---|---|
#UD | If the LOCK prefix is used. |
#NM | CR0.EM[bit 2] or CR0.TS[bit 3] = 1. |