x86 Instruction Set Reference

MAXSS

Return Maximum Scalar Single-Precision Floating-Point Value

Opcode Mnemonic Description
F3 0F 5F /r MAXSS xmm1, xmm2/m32 Return the maximum scalar single-precision floating-point value between xmm2/mem32 and xmm1.
Description

Compares the low single-precision floating-point values in the destination operand (first operand) and the source operand (second operand), and returns the maximum value to the low doubleword of the destination operand. The source operand can be an XMM register or a 32-bit memory location. The destination operand is an XMM register. When the source operand is a memory operand, only 32 bits are accessed. The three high-order doublewords of the destination operand remain unchanged.

If the values being compared are both 0.0s (of either sign), the value in the second operand (source operand) is returned. If a value in the second operand is an SNaN, that SNaN is returned unchanged to the destination (that is, a QNaN version of the SNaN is not returned).

If only one value is a NaN (SNaN or QNaN) for this instruction, the second operand (source operand), either a NaN or a valid floating-point value, is written to the result. If instead of this behavior, it is required that the NaN source operand (from either the first or second operand) be returned, the action of MAXSS can be emulated using a sequence of instructions, such as, a comparison followed by AND, ANDN and OR.
Operation 
if((Destination[0..31] == 0.0 && Source[0..31] == 0.0) || IsSNaN(Destination[0..31]) || IsSNaN(Source[0..31]) || Destination[0..31] <= Source[0..31]) Destination[0..31] = Source[0..31];
//Destination[32..127] is unchanged
SIMD Floating-Point Exceptions
Invalid(including QNaN source operand), Denormal.
Protected Mode Exceptions
#GP(0)For an illegal memory operand effective address in the CS, DS, ES, FS or GS segments.
#GP(0)For an illegal memory operand effective address in the CS, DS, ES, FS or GS segments.
#SS(0)If a memory operand effective address is outside the SS segment limit.
#PF(fault-code)For a page fault.
#NMIf TS in CR0 is set.
#XMIf an unmasked SIMD floating-point exception and OSXMMEXCPT in CR4 is 1.
#UDIf an unmasked SIMD floating-point exception and OSXMMEXCPT in CR4 is 0. If EM in CR0 is set. If OSFXSR in CR4 is 0. If CPUID feature flag SSE is 0.
Real-Address Mode Exceptions
#GP(0)If any part of the operand lies outside the effective address space from 0 to FFFFH.
#GP(0)If any part of the operand lies outside the effective address space from 0 to FFFFH.
#NMIf TS in CR0 is set.
#XMIf an unmasked SIMD floating-point exception and OSXMMEXCPT in CR4 is 1.
Virtual-8086 Mode Exceptions
Same exceptions as in Real Address Mode
#PF(fault-code)For a page fault.
#PF(fault-code)For a page fault.
Instruction Latency Throughput Execution Unit
CPUID0F3n/0F2n0F3n/0F2n0F2n
MAXSS xmm, xmm5/42/2FP_ADD