LDMXCSR (Load MXCSR Register)

Opcodes

Opcode/Instruction Op/En 64/32-bit Mode CPUID Feature Flag Description
0F,AE,/2 LDMXCSR m32 M V/V SSE Load MXCSR register from m32.
VEX.LZ.0F.WIG AE /2 VLDMXCSR m32 M V/V AVX Load MXCSR register from m32.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
M ModRM:r/m (r) NA NA NA

Description

Loads the source operand into the MXCSR control/status register. The source operand is a 32-bit memory location. See “MXCSR Control and Status Register” in Chapter 10, of the Intel® 64 and IA-32 Architectures Software Devel-oper’s Manual, Volume 1, for a description of the MXCSR register and its contents.

The LDMXCSR instruction is typically used in conjunction with the (V)STMXCSR instruction, which stores the contents of the MXCSR register in memory.

The default MXCSR value at reset is 1F80H.

If a (V)LDMXCSR instruction clears a SIMD floating-point exception mask bit and sets the corresponding exception flag bit, a SIMD floating-point exception will not be immediately generated. The exception will be generated only upon the execution of the next instruction that meets both conditions below:

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

If VLDMXCSR is encoded with VEX.L= 1, an attempt to execute the instruction encoded with VEX.L= 1 will cause an #UD exception.

Note: In VEX-encoded versions, VEX.vvvv is reserved and must be 1111b, otherwise instructions will #UD.

Operation

MXCSR ← m32;

C/C++ Compiler Intrinsic Equivalent

_mm_setcsr(unsigned int i)

Numeric Exceptions

None.

Other Exceptions

See Exceptions Type 5; additionally

#GP For an attempt to set reserved bits in MXCSR.
#UD If VEX.vvvv ≠ 1111B.