Dead zone code commonly occurs in real-time applications.

The code block below shows the the ternary operator '?' based approach to implementing dead zone code. The C29 (10 cycles, independent of input) outperforms the C28 (25-36 cycles, dependent on input) and Cortex-M7 (23-35 cycles, dependent on input). This efficiency is achieved through the delayed return instruction (RETD) and well-utilized delay slots containing compare (CMPF) and assignment (SELECT) instructions.

float deadzone(float in)
{
 float out; 
 float  out_pos = in - 1.0f;
 float  out_neg = in + 1.0f; 
 out = (in > 1.0f)?  out_pos : ((in > -1.0f)? 0.0f : out_neg); 
 return out; 
}
C29 Implementation
Function call:
CALL @deadzone 
|| LD.32 M0,@in1  
;---------CALLD occurs  
ST.32 @out1,M0  
 deadzone:
ONEF M1   
|| NEGONEF M2  
SADDF M3,M0,M2   
|| CMPF TDM0,M.GT,M0,M2  
|| SADDF M2,M0,M1  
|| RETD  
ZERO M4  
CMPF TDM1,M.GT,M0,M1  
|| SELECT TDM0,M0,M4,M2  
SELECT TDM1,M0,M3,M0  

C28 Implementation
Function call: MOVW  DP,#_in1 
MOV32 R0H,@_in1  
LCR   #_deadzone
MOVW  DP,#_out1   
MOV32 @_out1,R0H

_deadzone:
ADDB   SP,#2     
CMPF32 R0H,#16256
MOVST0 ZF, NF  
B      $C$L1,LEQ  
ADDF32 R0H,R0H,#49024  
B      $C$L3,UNC   
$C$L1:
CMPF32 R0H,#49024  
MOVST0 ZF, NF   
B      $C$L2,LEQ  
ZERO   R0H  
B      $C$L3,UNC   
$C$L2:
ADDF32 R0H,R0H,#16256   
$C$L3:
SUBB   SP,#2  
LRETR   

M7 Implementation
Function call:
VLDR  S0,[R6, #+144] 
BL    deadzone   
VSTR  S0,[R6, #+152] 
  
deadzone:
MOVS     R0,#+1   
MOVT     R0,#+16256   
VMOV     S2,R0   
VMOV.F32 S1,S0  
VCMP.F32 S1,S2  
FMSTAT  
VMOV.F32 S0,#1.0  
VADD.F32 S0,S1,S0  
BLT.N    deadzone_0   
VMOV.F32 S3,#-1.0  
VADD.F32 S0,S1,S3  
BX       LR   
deadzone_0:
MVN      R1,#+1082130432  
VMOV     S4,R1   
VCMP.F32 S1,S4  
FMSTAT  
ITT     GE   
MOVGE   R0,#+0   
VMOVGE  S0,R0   
BX      LR