Binary encoding of SIMD

This document describes the binary encoding of the SIMD value type and instructions.

SIMD value type

The v128 value type is encoded as 0x7b:

valtype ::= ...
          | 0x7B => v128

SIMD instruction encodings

All SIMD instructions are encoded as a 0xfd prefix byte followed by a SIMD-specific opcode in LEB128 format:

instr ::= ...
        | 0xFD simdop:varuint32 ...

Some SIMD instructions have additional immediate operands following simdop. These immediate operands are encoded as individual bytes. For example, the i8x16.shuffle instruction has 16 bytes after simdop.

In the description below, ImmLaneIdx{I} indicates the maximum value of the byte. For example, ImmLaneIdx16 is a byte with values in the range 0-15 (inclusive).

Instruction	`simdop`	Immediate operands
`v128.load`	`0x00`	m:memarg
`v128.load8x8_s`	`0x01`	m:memarg
`v128.load8x8_u`	`0x02`	m:memarg
`v128.load16x4_s`	`0x03`	m:memarg
`v128.load16x4_u`	`0x04`	m:memarg
`v128.load32x2_s`	`0x05`	m:memarg
`v128.load32x2_u`	`0x06`	m:memarg
`v128.load8_splat`	`0x07`	m:memarg
`v128.load16_splat`	`0x08`	m:memarg
`v128.load32_splat`	`0x09`	m:memarg
`v128.load64_splat`	`0x0a`	m:memarg
`v128.store`	`0x0b`	m:memarg
`v128.const`	`0x0c`	i:ImmByte[16]
`i8x16.shuffle`	`0x0d`	s:ImmLaneIdx32[16]
`i8x16.swizzle`	`0x0e`	-
`i8x16.splat`	`0x0f`	-
`i16x8.splat`	`0x10`	-
`i32x4.splat`	`0x11`	-
`i64x2.splat`	`0x12`	-
`f32x4.splat`	`0x13`	-
`f64x2.splat`	`0x14`	-
`i8x16.extract_lane_s`	`0x15`	i:ImmLaneIdx16
`i8x16.extract_lane_u`	`0x16`	i:ImmLaneIdx16
`i8x16.replace_lane`	`0x17`	i:ImmLaneIdx16
`i16x8.extract_lane_s`	`0x18`	i:ImmLaneIdx8
`i16x8.extract_lane_u`	`0x19`	i:ImmLaneIdx8
`i16x8.replace_lane`	`0x1a`	i:ImmLaneIdx8
`i32x4.extract_lane`	`0x1b`	i:ImmLaneIdx4
`i32x4.replace_lane`	`0x1c`	i:ImmLaneIdx4
`i64x2.extract_lane`	`0x1d`	i:ImmLaneIdx2
`i64x2.replace_lane`	`0x1e`	i:ImmLaneIdx2
`f32x4.extract_lane`	`0x1f`	i:ImmLaneIdx4
`f32x4.replace_lane`	`0x20`	i:ImmLaneIdx4
`f64x2.extract_lane`	`0x21`	i:ImmLaneIdx2
`f64x2.replace_lane`	`0x22`	i:ImmLaneIdx2
`i8x16.eq`	`0x23`	-
`i8x16.ne`	`0x24`	-
`i8x16.lt_s`	`0x25`	-
`i8x16.lt_u`	`0x26`	-
`i8x16.gt_s`	`0x27`	-
`i8x16.gt_u`	`0x28`	-
`i8x16.le_s`	`0x29`	-
`i8x16.le_u`	`0x2a`	-
`i8x16.ge_s`	`0x2b`	-
`i8x16.ge_u`	`0x2c`	-
`i16x8.eq`	`0x2d`	-
`i16x8.ne`	`0x2e`	-
`i16x8.lt_s`	`0x2f`	-
`i16x8.lt_u`	`0x30`	-
`i16x8.gt_s`	`0x31`	-
`i16x8.gt_u`	`0x32`	-
`i16x8.le_s`	`0x33`	-
`i16x8.le_u`	`0x34`	-
`i16x8.ge_s`	`0x35`	-
`i16x8.ge_u`	`0x36`	-
`i32x4.eq`	`0x37`	-
`i32x4.ne`	`0x38`	-
`i32x4.lt_s`	`0x39`	-
`i32x4.lt_u`	`0x3a`	-
`i32x4.gt_s`	`0x3b`	-
`i32x4.gt_u`	`0x3c`	-
`i32x4.le_s`	`0x3d`	-
`i32x4.le_u`	`0x3e`	-
`i32x4.ge_s`	`0x3f`	-
`i32x4.ge_u`	`0x40`	-
`f32x4.eq`	`0x41`	-
`f32x4.ne`	`0x42`	-
`f32x4.lt`	`0x43`	-
`f32x4.gt`	`0x44`	-
`f32x4.le`	`0x45`	-
`f32x4.ge`	`0x46`	-
`f64x2.eq`	`0x47`	-
`f64x2.ne`	`0x48`	-
`f64x2.lt`	`0x49`	-
`f64x2.gt`	`0x4a`	-
`f64x2.le`	`0x4b`	-
`f64x2.ge`	`0x4c`	-
`v128.not`	`0x4d`	-
`v128.and`	`0x4e`	-
`v128.andnot`	`0x4f`	-
`v128.or`	`0x50`	-
`v128.xor`	`0x51`	-
`v128.bitselect`	`0x52`	-
`i8x16.abs`	`0x60`	-
`i8x16.neg`	`0x61`	-
`i8x16.all_true`	`0x63`	-
`i8x16.bitmask`	`0x64`	-
`i8x16.narrow_i16x8_s`	`0x65`	-
`i8x16.narrow_i16x8_u`	`0x66`	-
`i8x16.shl`	`0x6b`	-
`i8x16.shr_s`	`0x6c`	-
`i8x16.shr_u`	`0x6d`	-
`i8x16.add`	`0x6e`	-
`i8x16.add_sat_s`	`0x6f`	-
`i8x16.add_sat_u`	`0x70`	-
`i8x16.sub`	`0x71`	-
`i8x16.sub_sat_s`	`0x72`	-
`i8x16.sub_sat_u`	`0x73`	-
`i8x16.min_s`	`0x76`	-
`i8x16.min_u`	`0x77`	-
`i8x16.max_s`	`0x78`	-
`i8x16.max_u`	`0x79`	-
`i8x16.avgr_u`	`0x7b`	-
`i16x8.abs`	`0x80`	-
`i16x8.neg`	`0x81`	-
`i16x8.all_true`	`0x83`	-
`i16x8.bitmask`	`0x84`	-
`i16x8.narrow_i32x4_s`	`0x85`	-
`i16x8.narrow_i32x4_u`	`0x86`	-
`i16x8.extend_low_i8x16_s`	`0x87`	-
`i16x8.extend_high_i8x16_s`	`0x88`	-
`i16x8.extend_low_i8x16_u`	`0x89`	-
`i16x8.extend_high_i8x16_u`	`0x8a`	-
`i16x8.shl`	`0x8b`	-
`i16x8.shr_s`	`0x8c`	-
`i16x8.shr_u`	`0x8d`	-
`i16x8.add`	`0x8e`	-
`i16x8.add_sat_s`	`0x8f`	-
`i16x8.add_sat_u`	`0x90`	-
`i16x8.sub`	`0x91`	-
`i16x8.sub_sat_s`	`0x92`	-
`i16x8.sub_sat_u`	`0x93`	-
`i16x8.mul`	`0x95`	-
`i16x8.min_s`	`0x96`	-
`i16x8.min_u`	`0x97`	-
`i16x8.max_s`	`0x98`	-
`i16x8.max_u`	`0x99`	-
`i16x8.avgr_u`	`0x9b`	-
`i32x4.abs`	`0xa0`	-
`i32x4.neg`	`0xa1`	-
`i32x4.all_true`	`0xa3`	-
`i32x4.bitmask`	`0xa4`	-
`i32x4.extend_low_i16x8_s`	`0xa7`	-
`i32x4.extend_high_i16x8_s`	`0xa8`	-
`i32x4.extend_low_i16x8_u`	`0xa9`	-
`i32x4.extend_high_i16x8_u`	`0xaa`	-
`i32x4.shl`	`0xab`	-
`i32x4.shr_s`	`0xac`	-
`i32x4.shr_u`	`0xad`	-
`i32x4.add`	`0xae`	-
`i32x4.sub`	`0xb1`	-
`i32x4.mul`	`0xb5`	-
`i32x4.min_s`	`0xb6`	-
`i32x4.min_u`	`0xb7`	-
`i32x4.max_s`	`0xb8`	-
`i32x4.max_u`	`0xb9`	-
`i32x4.dot_i16x8_s`	`0xba`	-
`i64x2.abs`	`0xc0`	-
`i64x2.neg`	`0xc1`	-
`i64x2.bitmask`	`0xc4`	-
`i64x2.extend_low_i32x4_s`	`0xc7`	-
`i64x2.extend_high_i32x4_s`	`0xc8`	-
`i64x2.extend_low_i32x4_u`	`0xc9`	-
`i64x2.extend_high_i32x4_u`	`0xca`	-
`i64x2.shl`	`0xcb`	-
`i64x2.shr_s`	`0xcc`	-
`i64x2.shr_u`	`0xcd`	-
`i64x2.add`	`0xce`	-
`i64x2.sub`	`0xd1`	-
`i64x2.mul`	`0xd5`	-
`f32x4.ceil`	`0x67`	-
`f32x4.floor`	`0x68`	-
`f32x4.trunc`	`0x69`	-
`f32x4.nearest`	`0x6a`	-
`f64x2.ceil`	`0x74`	-
`f64x2.floor`	`0x75`	-
`f64x2.trunc`	`0x7a`	-
`f64x2.nearest`	`0x94`	-
`f32x4.abs`	`0xe0`	-
`f32x4.neg`	`0xe1`	-
`f32x4.sqrt`	`0xe3`	-
`f32x4.add`	`0xe4`	-
`f32x4.sub`	`0xe5`	-
`f32x4.mul`	`0xe6`	-
`f32x4.div`	`0xe7`	-
`f32x4.min`	`0xe8`	-
`f32x4.max`	`0xe9`	-
`f32x4.pmin`	`0xea`	-
`f32x4.pmax`	`0xeb`	-
`f64x2.abs`	`0xec`	-
`f64x2.neg`	`0xed`	-
`f64x2.sqrt`	`0xef`	-
`f64x2.add`	`0xf0`	-
`f64x2.sub`	`0xf1`	-
`f64x2.mul`	`0xf2`	-
`f64x2.div`	`0xf3`	-
`f64x2.min`	`0xf4`	-
`f64x2.max`	`0xf5`	-
`f64x2.pmin`	`0xf6`	-
`f64x2.pmax`	`0xf7`	-
`i32x4.trunc_sat_f32x4_s`	`0xf8`	-
`i32x4.trunc_sat_f32x4_u`	`0xf9`	-
`f32x4.convert_i32x4_s`	`0xfa`	-
`f32x4.convert_i32x4_u`	`0xfb`	-
`v128.load32_zero`	`0x5c`	m:memarg
`v128.load64_zero`	`0x5d`	m:memarg
`i16x8.extmul_low_i8x16_s`	`0x9c`	-
`i16x8.extmul_high_i8x16_s`	`0x9d`	-
`i16x8.extmul_low_i8x16_u`	`0x9e`	-
`i16x8.extmul_high_i8x16_u`	`0x9f`	-
`i32x4.extmul_low_i16x8_s`	`0xbc`	-
`i32x4.extmul_high_i16x8_s`	`0xbd`	-
`i32x4.extmul_low_i16x8_u`	`0xbe`	-
`i32x4.extmul_high_i16x8_u`	`0xbf`	-
`i64x2.extmul_low_i32x4_s`	`0xdc`	-
`i64x2.extmul_high_i32x4_s`	`0xdd`	-
`i64x2.extmul_low_i32x4_u`	`0xde`	-
`i64x2.extmul_high_i32x4_u`	`0xdf`	-
`i16x8.q15mulr_sat_s`	`0x82`	-
`v128.any_true`	`0x53`	-
`v128.load8_lane`	`0x54`	m:memarg, i:ImmLaneIdx16
`v128.load16_lane`	`0x55`	m:memarg, i:ImmLaneIdx8
`v128.load32_lane`	`0x56`	m:memarg, i:ImmLaneIdx4
`v128.load64_lane`	`0x57`	m:memarg, i:ImmLaneIdx2
`v128.store8_lane`	`0x58`	m:memarg, i:ImmLaneIdx16
`v128.store16_lane`	`0x59`	m:memarg, i:ImmLaneIdx8
`v128.store32_lane`	`0x5a`	m:memarg, i:ImmLaneIdx4
`v128.store64_lane`	`0x5b`	m:memarg, i:ImmLaneIdx2
`i64x2.eq`	`0xd6`	-
`i64x2.ne`	`0xd7`	-
`i64x2.lt_s`	`0xd8`	-
`i64x2.gt_s`	`0xd9`	-
`i64x2.le_s`	`0xda`	-
`i64x2.ge_s`	`0xdb`	-
`i64x2.all_true`	`0xc3`	-
`f64x2.convert_low_i32x4_s`	`0xfe`	-
`f64x2.convert_low_i32x4_u`	`0xff`	-
`i32x4.trunc_sat_f64x2_s_zero`	`0xfc`	-
`i32x4.trunc_sat_f64x2_u_zero`	`0xfd`	-
`f32x4.demote_f64x2_zero`	`0x5e`	-
`f64x2.promote_low_f32x4`	`0x5f`	-
`i8x16.popcnt`	`0x62`	-
`i16x8.extadd_pairwise_i8x16_s`	`0x7c`	-
`i16x8.extadd_pairwise_i8x16_u`	`0x7d`	-
`i32x4.extadd_pairwise_i16x8_s`	`0x7e`	-
`i32x4.extadd_pairwise_i16x8_u`	`0x7f`	-