ldmxcsr

Load MXCSR Register

LDMXCSR m32

Loads the MXCSR control/status register from memory.

Details

Loads the MXCSR control and status register from a 32-bit memory operand, updating all SSE floating-point rounding modes, exception masks, exception flags, and DAZ/FTZ controls. This instruction serializes the CPU pipeline on many implementations. The instruction is available in 64-bit and protected modes with SSE support.

Pseudocode Operation

MXCSR ← [m32]

Example

LDMXCSR [rbp-4]

Encoding

Binary Layout
0F
+0
AE
+1
ModRM
+2
 
Format SSE
Opcode NP 0F AE /2
Extension SSE

Operands

  • dest
    32-bit memory operand

Reference (Intel® SDM)

Instruction Forms

Opcode Instruction Op/En 64/32-bit Mode CPUID Description
NP 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.

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 Developer’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: • the instruction must operate on an XMM or YMM register operand, • the instruction causes that particular SIMD floating-point exception to be reported. 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)

Exceptions

Other Exceptions

See Table 2-22, “Type 5 Class Exception Conditions,” additionally: #GP For an attempt to set reserved bits in MXCSR. #UD If VEX.vvvv ≠ 1111B. LDMXCSR—Load MXCSR Register Vol. 2A 3-539

Numeric Exceptions

None.