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1.3.6 Floating-point Exceptions (FPE)
Floating-point Exception (FPE) occurs when Unimplemented Exception (UIPL) or
one of the five exceptions specified in the IEEE754 standard (OVF/UDF/IXCT/
DIV0/IVLD) is detected. Each exception processing is outlined below.
(1) Overflow Exception (OVF)
The exception occurs when the absolute value of the operation result exceeds the
largest describable precision in the floating-point format. The following table shows
the operation results when an OVF occurs.
Rounding Mode
Sign of the Result
–infinity
+
–
+infinity
+
–
0
+
–
Nearest
+
–
Note 1: When the Overflow Exception Enable (EO) bit (FPSR register bit 20) = "0"
Note 2: When the Overflow Exception Enable (EO) bit (FPSR register bit 20) = "1"
Note: • If an OVF occurs while EIT processing for OVF is masked, an IXCT occurs at the same time.
• +MAX = H'7F7F FFFF, –MAX = H'FF7F FFFF
(2) Underflow Exception (UDF)
The exception occurs when the absolute value of the operation result is less than
the largest describable precision in the floating-point format. The following table
shows the operation results when a UDF occurs.
When UDF EIT processing is masked (Note 1)
DN = 0: An unimplemented exception occurs
DN = 1: 0 is returned
Note 1: When the Underflow Exception Enable (EU) bit (FPSR register bit 18) = "0"
Note 2: When the Underflow Exception Enable (EU) bit (FPSR register bit 18) = "1"
CPU PROGRAMMING MODEL
Operation Result (Content of the Destination Register)
When the OVF EIT processing
is masked (Note 1)
+MAX
–infinity
+infinity
–MAX
+MAX
–MAX
+infinity
–infinity
Operation Result (Content of the Destination Register)
1-8
When the OVF EIT processing
is executed (Note 2)
No change
When UDF EIT processing is executed (Note 2)
No change
M32R-FPU Software Manual (Rev.1.01)
1.3 Control Registers
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