comisd
Compare Scalar Ordered Double-Precision
Compares low double and sets EFLAGS (Signaling NaN raises exception).
Pseudocode Operation
src1_val ← src1[0:63] (as double); src2_val ← src2[0:63] (as double); if (IsNaN(src1_val) || IsNaN(src2_val)) { ZF ← 1; PF ← 1; CF ← 1; OF ← 0; AF ← 0; SF ← 0; } else if (src1_val < src2_val) { CF ← 1; ZF ← 0; PF ← 0; OF ← 0; AF ← 0; SF ← 0; } else if (src1_val == src2_val) { ZF ← 1; CF ← 0; PF ← 0; OF ← 0; AF ← 0; SF ← 0; } else { ZF ← 0; CF ← 0; PF ← 0; OF ← 0; AF ← 0; SF ← 0; }Encoding
Operands
-
src1
XMM -
src2
XMM/Mem
Related
More in SSE2
Reference
Instruction Forms
| Opcode | Instruction | Op/En | 64/32-bit Mode | CPUID | Description |
|---|---|---|---|---|---|
| 66 0F 2F /r | COMISD xmm1, xmm2/m64 | A | V/V | SSE2 | Compare low double precision floating-point values in xmm1 and xmm2/mem64 and set the EFLAGS flags accordingly. |
| VEX.LIG.66.0F.WIG 2F /r | VCOMISD xmm1, xmm2/m64 | A | V/V | AVX | Compare low double precision floating-point values in xmm1 and xmm2/mem64 and set the EFLAGS flags accordingly. |
| EVEX.LLIG.66.0F.W1 2F /r | VCOMISD xmm1, xmm2/m64{sae} | B | V/V | AVX512F OR AVX10.1 | Compare low double precision floating-point values in xmm1 and xmm2/mem64 and set the EFLAGS flags accordingly. |
Instruction Operand Encoding
| Op/En | Tuple Type | Operand 1 | Operand 2 | Operand 3 | Operand 4 |
|---|---|---|---|---|---|
| A | N/A | ModRM:reg (w) | ModRM:r/m (r) | N/A | N/A |
| B | Tuple1 Scalar | ModRM:reg (w) | ModRM:r/m (r) | N/A | N/A |
Description
Compares the double precision floating-point values in the low quadwords of operand 1 (first operand) and operand 2 (second operand), and sets the ZF, PF, and CF flags in the EFLAGS register according to the result (unordered, greater than, less than, or equal). The OF, SF, and AF flags in the EFLAGS register are set to 0. The unordered result is returned if either source operand is a NaN (QNaN or SNaN). Operand 1 is an XMM register; operand 2 can be an XMM register or a 64 bit memory location. The COMISD instruction differs from the UCOMISD instruction in that it signals a SIMD floating-point invalid operation exception (#I) when a source operand is either a QNaN or SNaN. The UCOMISD instruction signals an invalid operation exception only if a source operand is an SNaN. The EFLAGS register is not updated if an unmasked SIMD floating-point exception is generated. VEX.vvvv and EVEX.vvvv are reserved and must be 1111b, otherwise instructions will #UD. Software should ensure VCOMISD is encoded with VEX.L=0. Encoding VCOMISD with VEX.L=1 may encounter unpredictable behavior across different processor generations.
Operation
COMISD (All Versions)
RESULT :=OrderedCompare(DEST[63:0] <> SRC[63:0]) {
(* Set EFLAGS *) CASE (RESULT) OF
UNORDERED: ZF,PF,CF := 111;
GREATER_THAN: ZF,PF,CF := 000;
LESS_THAN: ZF,PF,CF := 001;
EQUAL: ZF,PF,CF := 100;
ESAC;
OF, AF, SF := 0; }Intel C/C++ Compiler Intrinsic Equivalent
VCOMISD int _mm_comi_round_sd(__m128d a, __m128d b, int imm, int sae); VCOMISD int _mm_comieq_sd (__m128d a, __m128d b) VCOMISD int _mm_comilt_sd (__m128d a, __m128d b) VCOMISD int _mm_comile_sd (__m128d a, __m128d b) VCOMISD int _mm_comigt_sd (__m128d a, __m128d b) VCOMISD int _mm_comige_sd (__m128d a, __m128d b) VCOMISD int _mm_comineq_sd (__m128d a, __m128d b)