Renesas M32R-FPU Manual Do Utilizador

APPENDICES

APPENDICES-23

M32R-FPU Software Manual (Rev.1.01)

Appendix 6 M32R-FPU Specification Supplemental Explanation

Appendix 6.1 Operation Comparision: Using 1 instruction (FMADD or FMSBU) vs. two

instructions (FMUL and FADD)

The following is an explanation of the differences between an operation using just one

instruction (FMADD or FMSUB) and an operation using 2 instructions (FMUL and

FADD).

Appendix 6.1.1 Rounding Mode

The rounding mode for an operation using both FMUL and FADD rounds both FMUL

and FADD according to the setting of the FPSR RM field. However, the result of the

FMADD or FMSUB instruction in Step 1 (multiply stage) is not rounded according to

the setting of FPSR RM field, rather it is rounded toward zero.

Appendix 6.1.2 Exception occurring in Step 1

Two instructions are compared below as examples of Exception occurring in Step 1.

● 

FMUL + FADD:

FMUL

R3, R1, R2

(R3 = R1 * R2)

FADD

R0, R3, R0

(R0 = R3 + R0)

● 

FMADD or FMSUB:

FMADD

R0, R1, R2

(R0 = R0 +R1 * R2)

Note: If the register supports different operations than those described above, the

 operations may differ in some ways to those shown below.

APPENDIX 6

Appendix 6 M32R-FPU Specification Supplemental Explanation