Renesas M32R-FPU - Manual (Page 181)

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