FSQRT

Square Root

Opcodes

Hex Mnemonic Encoding Long Mode Legacy Mode Description
D9 FA FSQRT None Valid Valid Computes square root of ST(0) and stores the result in ST(0).

Description

Computes the square root of the source value in the ST(0) register and stores the result in ST(0).

The following table shows the results obtained when taking the square root of various classes of numbers, assuming that neither overflow nor underflow occurs.

FSQRT Results
SRC (ST(0)) DEST (ST(0))
-∞ *
- F *
- 0 - 0
+ 0 + 0
+ F + F
+∞ +∞
NaN NaN

This instruction's operation is the same in non-64-bit modes and 64-bit mode.

Pseudo Code

ST(0) = SquareRoot(ST(0));

FPU Flags Affected

C1: Set to 0 if stack underflow occurred. Set if result was rounded up; cleared otherwise. C0, C2, C3 are undefined.

Exceptions

Floating-Point Exceptions

Exception Description
#P Value cannot be represented exactly in destination format.
#D Source operand is a denormal value.
#IA Source operand is an SNaN value or unsupported format. Source operand is a negative value (except for -0).
#IS Stack underflow occurred.

64-Bit Mode Exceptions

Same exceptions as in protected mode.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

Virtual-8086 Mode Exceptions

Same exceptions as in protected mode.

Real-Address Mode Exceptions

Same exceptions as in protected mode.

Protected Mode Exceptions

Exception Description
#UD If the LOCK prefix is used.
#MF If there is a pending x87 FPU exception.
#NM CR0.EM[bit 2] or CR0.TS[bit 3] = 1.