diff --git a/zstd/_generate/gen.go b/zstd/_generate/gen.go
index 7ef9a45aa8..03a3595d4a 100644
--- a/zstd/_generate/gen.go
+++ b/zstd/_generate/gen.go
@@ -316,7 +316,7 @@ func (o options) generateBody(name string, executeSingleTriple func(ctx *execute
 				lowBits := GP64()
 				BZHIQ(nBits, bits, lowBits) // lowBits = bits & ((1 << nBits) - 1))
 				SHRXQ(nBits, bits, bits)    // bits >>= nBits
-				o.nextState(name+"_ofState", ofState, lowBits, "ofTable")
+				o.nextState(ofState, lowBits, "ofTable")
 			}
 			Comment("Update Match Length State")
 			{
@@ -324,22 +324,22 @@ func (o options) generateBody(name string, executeSingleTriple func(ctx *execute
 				lowBits := GP64()
 				BZHIQ(nBits, bits, lowBits) // lowBits = bits & ((1 << nBits) - 1))
 				SHRXQ(nBits, bits, bits)    // lowBits >>= nBits
-				o.nextState(name+"_mlState", mlState, lowBits, "mlTable")
+				o.nextState(mlState, lowBits, "mlTable")
 			}
 			Comment("Update Literal Length State")
 			{
 				nBits := llState
 				lowBits := GP64()
 				BZHIQ(nBits, bits, lowBits) // lowBits = bits & ((1 << nBits) - 1))
-				o.nextState(name+"_llState", llState, lowBits, "llTable")
+				o.nextState(llState, lowBits, "llTable")
 			}
 		} else {
 			Comment("Update Literal Length State")
-			o.updateState(name+"_llState", llState, brValue, brBitsRead, "llTable")
+			o.updateState(llState, brValue, brBitsRead, "llTable")
 			Comment("Update Match Length State")
-			o.updateState(name+"_mlState", mlState, brValue, brBitsRead, "mlTable")
+			o.updateState(mlState, brValue, brBitsRead, "mlTable")
 			Comment("Update Offset State")
-			o.updateState(name+"_ofState", ofState, brValue, brBitsRead, "ofTable")
+			o.updateState(ofState, brValue, brBitsRead, "ofTable")
 		}
 	}
 	Label(name + "_skip_update")
@@ -631,8 +631,7 @@ func (o options) updateLength(name string, brValue, brBitsRead, state reg.GPVirt
 	}
 }
 
-func (o options) updateState(name string, state, brValue, brBitsRead reg.GPVirtual, table string) {
-	name = name + "_updateState"
+func (o options) updateState(state, brValue, brBitsRead reg.GPVirtual, table string) {
 	AX := GP64()
 	MOVBQZX(state.As8(), AX) // AX = nBits
 	// Check we have a reasonable nBits
@@ -642,15 +641,8 @@ func (o options) updateState(name string, state, brValue, brBitsRead reg.GPVirtu
 	})
 
 	DX := GP64()
-	if o.bmi2 {
-		tmp := GP64()
-		MOVQ(U32(16|(16<<8)), tmp)
-		BEXTRQ(tmp, state, DX)
-	} else {
-		MOVQ(state, DX)
-		SHRQ(U8(16), DX)
-		MOVWQZX(DX.As16(), DX)
-	}
+	MOVL(state.As32(), DX.As32()) // Clear the top 32 bits.
+	SHRL(U8(16), DX.As32())
 
 	{
 		lowBits := o.getBits(AX, brValue, brBitsRead)
@@ -681,17 +673,10 @@ func (o options) updateState(name string, state, brValue, brBitsRead reg.GPVirtu
 	MOVQ(Mem{Base: tablePtr, Index: DX, Scale: 8}, state)
 }
 
-func (o options) nextState(name string, state, lowBits reg.GPVirtual, table string) {
+func (o options) nextState(state, lowBits reg.GPVirtual, table string) {
 	DX := GP64()
-	if o.bmi2 {
-		tmp := GP64()
-		MOVQ(U32(16|(16<<8)), tmp)
-		BEXTRQ(tmp, state, DX)
-	} else {
-		MOVQ(state, DX)
-		SHRQ(U8(16), DX)
-		MOVWQZX(DX.As16(), DX)
-	}
+	MOVL(state.As32(), DX.As32()) // Clear the top 32 bits.
+	SHRL(U8(16), DX.As32())
 
 	ADDQ(lowBits, DX)
 
diff --git a/zstd/seqdec_amd64.s b/zstd/seqdec_amd64.s
index 974b99725f..5b06174b89 100644
--- a/zstd/seqdec_amd64.s
+++ b/zstd/seqdec_amd64.s
@@ -157,8 +157,7 @@ sequenceDecs_decode_amd64_ll_update_zero:
 
 	// Update Literal Length State
 	MOVBQZX DI, R14
-	SHRQ    $0x10, DI
-	MOVWQZX DI, DI
+	SHRL    $0x10, DI
 	LEAQ    (BX)(R14*1), CX
 	MOVQ    DX, R15
 	MOVQ    CX, BX
@@ -177,8 +176,7 @@ sequenceDecs_decode_amd64_ll_update_zero:
 
 	// Update Match Length State
 	MOVBQZX R8, R14
-	SHRQ    $0x10, R8
-	MOVWQZX R8, R8
+	SHRL    $0x10, R8
 	LEAQ    (BX)(R14*1), CX
 	MOVQ    DX, R15
 	MOVQ    CX, BX
@@ -197,8 +195,7 @@ sequenceDecs_decode_amd64_ll_update_zero:
 
 	// Update Offset State
 	MOVBQZX R9, R14
-	SHRQ    $0x10, R9
-	MOVWQZX R9, R9
+	SHRL    $0x10, R9
 	LEAQ    (BX)(R14*1), CX
 	MOVQ    DX, R15
 	MOVQ    CX, BX
@@ -459,8 +456,7 @@ sequenceDecs_decode_56_amd64_ll_update_zero:
 
 	// Update Literal Length State
 	MOVBQZX DI, R14
-	SHRQ    $0x10, DI
-	MOVWQZX DI, DI
+	SHRL    $0x10, DI
 	LEAQ    (BX)(R14*1), CX
 	MOVQ    DX, R15
 	MOVQ    CX, BX
@@ -479,8 +475,7 @@ sequenceDecs_decode_56_amd64_ll_update_zero:
 
 	// Update Match Length State
 	MOVBQZX R8, R14
-	SHRQ    $0x10, R8
-	MOVWQZX R8, R8
+	SHRL    $0x10, R8
 	LEAQ    (BX)(R14*1), CX
 	MOVQ    DX, R15
 	MOVQ    CX, BX
@@ -499,8 +494,7 @@ sequenceDecs_decode_56_amd64_ll_update_zero:
 
 	// Update Offset State
 	MOVBQZX R9, R14
-	SHRQ    $0x10, R9
-	MOVWQZX R9, R9
+	SHRL    $0x10, R9
 	LEAQ    (BX)(R14*1), CX
 	MOVQ    DX, R15
 	MOVQ    CX, BX
@@ -772,11 +766,10 @@ sequenceDecs_decode_bmi2_fill_2_end:
 	BZHIQ   R14, R15, R15
 
 	// Update Offset State
-	BZHIQ  R8, R15, CX
-	SHRXQ  R8, R15, R15
-	MOVQ   $0x00001010, R14
-	BEXTRQ R14, R8, R8
-	ADDQ   CX, R8
+	BZHIQ R8, R15, CX
+	SHRXQ R8, R15, R15
+	SHRL  $0x10, R8
+	ADDQ  CX, R8
 
 	// Load ctx.ofTable
 	MOVQ ctx+16(FP), CX
@@ -784,11 +777,10 @@ sequenceDecs_decode_bmi2_fill_2_end:
 	MOVQ (CX)(R8*8), R8
 
 	// Update Match Length State
-	BZHIQ  DI, R15, CX
-	SHRXQ  DI, R15, R15
-	MOVQ   $0x00001010, R14
-	BEXTRQ R14, DI, DI
-	ADDQ   CX, DI
+	BZHIQ DI, R15, CX
+	SHRXQ DI, R15, R15
+	SHRL  $0x10, DI
+	ADDQ  CX, DI
 
 	// Load ctx.mlTable
 	MOVQ ctx+16(FP), CX
@@ -796,10 +788,9 @@ sequenceDecs_decode_bmi2_fill_2_end:
 	MOVQ (CX)(DI*8), DI
 
 	// Update Literal Length State
-	BZHIQ  SI, R15, CX
-	MOVQ   $0x00001010, R14
-	BEXTRQ R14, SI, SI
-	ADDQ   CX, SI
+	BZHIQ SI, R15, CX
+	SHRL  $0x10, SI
+	ADDQ  CX, SI
 
 	// Load ctx.llTable
 	MOVQ ctx+16(FP), CX
@@ -1032,11 +1023,10 @@ sequenceDecs_decode_56_bmi2_fill_end:
 	BZHIQ   R14, R15, R15
 
 	// Update Offset State
-	BZHIQ  R8, R15, CX
-	SHRXQ  R8, R15, R15
-	MOVQ   $0x00001010, R14
-	BEXTRQ R14, R8, R8
-	ADDQ   CX, R8
+	BZHIQ R8, R15, CX
+	SHRXQ R8, R15, R15
+	SHRL  $0x10, R8
+	ADDQ  CX, R8
 
 	// Load ctx.ofTable
 	MOVQ ctx+16(FP), CX
@@ -1044,11 +1034,10 @@ sequenceDecs_decode_56_bmi2_fill_end:
 	MOVQ (CX)(R8*8), R8
 
 	// Update Match Length State
-	BZHIQ  DI, R15, CX
-	SHRXQ  DI, R15, R15
-	MOVQ   $0x00001010, R14
-	BEXTRQ R14, DI, DI
-	ADDQ   CX, DI
+	BZHIQ DI, R15, CX
+	SHRXQ DI, R15, R15
+	SHRL  $0x10, DI
+	ADDQ  CX, DI
 
 	// Load ctx.mlTable
 	MOVQ ctx+16(FP), CX
@@ -1056,10 +1045,9 @@ sequenceDecs_decode_56_bmi2_fill_end:
 	MOVQ (CX)(DI*8), DI
 
 	// Update Literal Length State
-	BZHIQ  SI, R15, CX
-	MOVQ   $0x00001010, R14
-	BEXTRQ R14, SI, SI
-	ADDQ   CX, SI
+	BZHIQ SI, R15, CX
+	SHRL  $0x10, SI
+	ADDQ  CX, SI
 
 	// Load ctx.llTable
 	MOVQ ctx+16(FP), CX
@@ -1967,8 +1955,7 @@ sequenceDecs_decodeSync_amd64_ll_update_zero:
 
 	// Update Literal Length State
 	MOVBQZX DI, R13
-	SHRQ    $0x10, DI
-	MOVWQZX DI, DI
+	SHRL    $0x10, DI
 	LEAQ    (BX)(R13*1), CX
 	MOVQ    DX, R14
 	MOVQ    CX, BX
@@ -1987,8 +1974,7 @@ sequenceDecs_decodeSync_amd64_ll_update_zero:
 
 	// Update Match Length State
 	MOVBQZX R8, R13
-	SHRQ    $0x10, R8
-	MOVWQZX R8, R8
+	SHRL    $0x10, R8
 	LEAQ    (BX)(R13*1), CX
 	MOVQ    DX, R14
 	MOVQ    CX, BX
@@ -2007,8 +1993,7 @@ sequenceDecs_decodeSync_amd64_ll_update_zero:
 
 	// Update Offset State
 	MOVBQZX R9, R13
-	SHRQ    $0x10, R9
-	MOVWQZX R9, R9
+	SHRL    $0x10, R9
 	LEAQ    (BX)(R13*1), CX
 	MOVQ    DX, R14
 	MOVQ    CX, BX
@@ -2514,11 +2499,10 @@ sequenceDecs_decodeSync_bmi2_fill_2_end:
 	BZHIQ   R13, R14, R14
 
 	// Update Offset State
-	BZHIQ  R8, R14, CX
-	SHRXQ  R8, R14, R14
-	MOVQ   $0x00001010, R13
-	BEXTRQ R13, R8, R8
-	ADDQ   CX, R8
+	BZHIQ R8, R14, CX
+	SHRXQ R8, R14, R14
+	SHRL  $0x10, R8
+	ADDQ  CX, R8
 
 	// Load ctx.ofTable
 	MOVQ ctx+16(FP), CX
@@ -2526,11 +2510,10 @@ sequenceDecs_decodeSync_bmi2_fill_2_end:
 	MOVQ (CX)(R8*8), R8
 
 	// Update Match Length State
-	BZHIQ  DI, R14, CX
-	SHRXQ  DI, R14, R14
-	MOVQ   $0x00001010, R13
-	BEXTRQ R13, DI, DI
-	ADDQ   CX, DI
+	BZHIQ DI, R14, CX
+	SHRXQ DI, R14, R14
+	SHRL  $0x10, DI
+	ADDQ  CX, DI
 
 	// Load ctx.mlTable
 	MOVQ ctx+16(FP), CX
@@ -2538,10 +2521,9 @@ sequenceDecs_decodeSync_bmi2_fill_2_end:
 	MOVQ (CX)(DI*8), DI
 
 	// Update Literal Length State
-	BZHIQ  SI, R14, CX
-	MOVQ   $0x00001010, R13
-	BEXTRQ R13, SI, SI
-	ADDQ   CX, SI
+	BZHIQ SI, R14, CX
+	SHRL  $0x10, SI
+	ADDQ  CX, SI
 
 	// Load ctx.llTable
 	MOVQ ctx+16(FP), CX
@@ -3055,8 +3037,7 @@ sequenceDecs_decodeSync_safe_amd64_ll_update_zero:
 
 	// Update Literal Length State
 	MOVBQZX DI, R13
-	SHRQ    $0x10, DI
-	MOVWQZX DI, DI
+	SHRL    $0x10, DI
 	LEAQ    (BX)(R13*1), CX
 	MOVQ    DX, R14
 	MOVQ    CX, BX
@@ -3075,8 +3056,7 @@ sequenceDecs_decodeSync_safe_amd64_ll_update_zero:
 
 	// Update Match Length State
 	MOVBQZX R8, R13
-	SHRQ    $0x10, R8
-	MOVWQZX R8, R8
+	SHRL    $0x10, R8
 	LEAQ    (BX)(R13*1), CX
 	MOVQ    DX, R14
 	MOVQ    CX, BX
@@ -3095,8 +3075,7 @@ sequenceDecs_decodeSync_safe_amd64_ll_update_zero:
 
 	// Update Offset State
 	MOVBQZX R9, R13
-	SHRQ    $0x10, R9
-	MOVWQZX R9, R9
+	SHRL    $0x10, R9
 	LEAQ    (BX)(R13*1), CX
 	MOVQ    DX, R14
 	MOVQ    CX, BX
@@ -3704,11 +3683,10 @@ sequenceDecs_decodeSync_safe_bmi2_fill_2_end:
 	BZHIQ   R13, R14, R14
 
 	// Update Offset State
-	BZHIQ  R8, R14, CX
-	SHRXQ  R8, R14, R14
-	MOVQ   $0x00001010, R13
-	BEXTRQ R13, R8, R8
-	ADDQ   CX, R8
+	BZHIQ R8, R14, CX
+	SHRXQ R8, R14, R14
+	SHRL  $0x10, R8
+	ADDQ  CX, R8
 
 	// Load ctx.ofTable
 	MOVQ ctx+16(FP), CX
@@ -3716,11 +3694,10 @@ sequenceDecs_decodeSync_safe_bmi2_fill_2_end:
 	MOVQ (CX)(R8*8), R8
 
 	// Update Match Length State
-	BZHIQ  DI, R14, CX
-	SHRXQ  DI, R14, R14
-	MOVQ   $0x00001010, R13
-	BEXTRQ R13, DI, DI
-	ADDQ   CX, DI
+	BZHIQ DI, R14, CX
+	SHRXQ DI, R14, R14
+	SHRL  $0x10, DI
+	ADDQ  CX, DI
 
 	// Load ctx.mlTable
 	MOVQ ctx+16(FP), CX
@@ -3728,10 +3705,9 @@ sequenceDecs_decodeSync_safe_bmi2_fill_2_end:
 	MOVQ (CX)(DI*8), DI
 
 	// Update Literal Length State
-	BZHIQ  SI, R14, CX
-	MOVQ   $0x00001010, R13
-	BEXTRQ R13, SI, SI
-	ADDQ   CX, SI
+	BZHIQ SI, R14, CX
+	SHRL  $0x10, SI
+	ADDQ  CX, SI
 
 	// Load ctx.llTable
 	MOVQ ctx+16(FP), CX