X86 Registers, Flags, ....

1. x86 Register Encodings (Used in Machine Code)

Registers in x86 are not accessed directly via hex opcodes; instead, their usage is encoded in modR/M, SIB, or opcode bytes. Below is how they’re represented in 3-bit binary (and hex) within instruction fields.

Register	Binary	Hex (for internal encoding)	8-bit	16-bit	32-bit	64-bit
RAX	000	0x00	AL	AX	EAX	RAX
RCX	001	0x01	CL	CX	ECX	RCX
RDX	010	0x02	DL	DX	EDX	RDX
RBX	011	0x03	BL	BX	EBX	RBX
RSP	100	0x04	AH	SP	ESP	RSP
RBP	101	0x05	CH	BP	EBP	RBP
RSI	110	0x06	DH	SI	ESI	RSI
RDI	111	0x07	BH	DI	EDI	RDI

Registers R8–R15 are encoded using REX prefixes in 64-bit mode.

2. EFLAGS Register (Bit Positions and Hex Masks)

The EFLAGS register is a 32-bit register, where each flag is a single bit:

Bit	Hex Mask	Flag Name	Abbreviation	Description
0	0x00000001	Carry Flag	CF	Carry or borrow in arithmetic
2	0x00000004	Parity Flag	PF	Even parity of last result
4	0x00000010	Auxiliary Carry	AF	Carry from bit 3
6	0x00000040	Zero Flag	ZF	Result was zero
7	0x00000080	Sign Flag	SF	Result was negative
8	0x00000100	Trap Flag	TF	Step-by-step mode
9	0x00000200	Interrupt Enable	IF	Enable/disable interrupts
10	0x00000400	Direction Flag	DF	String operations direction
11	0x00000800	Overflow Flag	OF	Overflow in signed arithmetic

3. Machine Code (Hex) of AI / SIMD Instructions

These are specific hex opcodes used in AI and SIMD operations. The ModR/M byte (/r) specifies the register operands.

SSE (Streaming SIMD Extensions)

Instruction	Opcode (Hex)	Description
`ADDPS xmm1, xmm2`	`0F 58 /r`	Add packed single-precision floats
`SUBPS xmm1, xmm2`	`0F 5C /r`	Subtract packed floats
`MULPS xmm1, xmm2`	`0F 59 /r`	Multiply packed floats
`DIVPS xmm1, xmm2`	`0F 5E /r`	Divide packed floats
`MOVAPS xmm1, xmm2`	`0F 28 /r`	Move aligned packed float

AVX (Advanced Vector Extensions)

AVX uses a VEX prefix and works on 128/256-bit registers.

Instruction	VEX Prefix + Opcode	Description
`VADDPS ymm1, ymm2, ymm3`	`C5 F8 58 /r`	Add packed single-precision floats
`VMULPS ymm1, ymm2, ymm3`	`C5 F8 59 /r`	Multiply packed floats
`VSUBPS ymm1, ymm2, ymm3`	`C5 F8 5C /r`	Subtract packed floats

AMX (Advanced Matrix Extensions – Intel 2023+)

Tile-based instructions for deep learning acceleration:

Instruction	Hex (Encoding)	Description
`TILELOADD`	0xC4...	Load tile register (long encoding)
`TILESTORED`	0xC4...	Store tile register to memory
`TDPBSSD`	0xC4...	Dot-product of signed int8 with saturation

(Full hex depends on operands and is vendor-specific, typically long VEX-encoded.)

Example: Encoding `ADD EAX, EBX`

Instruction: ADD EAX, EBX
Opcode: 01 D8
- 01 is the opcode for ADD r/m32, r32
- D8 is the ModR/M byte (11 011 000) = EBX to EAX

Summary

Register references are encoded in binary (ModR/M or opcode bits), typically not standalone hex.
Flags in EFLAGS are set/cleared by instructions and are identified by bit and hex mask.
AI/SIMD instructions are encoded using specific hex opcodes (like 0F 58 /r) and VEX prefixes for AVX.