Freescale Semiconductor MC68881 - MC68881;MC68882 FPSR Quotient Byte; MC68881;MC68882 FPSR Exception Status Byte

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2.3.2 FPSR Quotient Byte
The quotient byte (see Figure 2-5) is set at the completion of the modulo (FMOD) or IEEE
remainder (FREM) instructions. This byte contains the seven least significant bits of the
quotient (unsigned) and the sign of the entire quotient.
23 22 21 20 19 18 17 It]
QUOTIENT
Figure 2-5. MC68881/MC68882 FPSR Quotient Byte
SEVEN LEAST SIGk'~FICAh'T
BITS OF IIUOIIENT
SIGN OF OUOTJEh"r
The quotient bits can be used in argument reduction for transcendentals and other func-
tions. For example, seven bits are more than enough to determine the quadrant of a circle
in which an operand resides. The quotient bits remain set until they are cleared by the
user, or until another FMOD or FREM instruction is executed.
2.3.3 FPSR Exception Status Byte
The exception status byte (EXC), shown in Figure 2-6, contains a bit for each floating-point
exception that may have occurred during the most recent arithmetic instruction or move
operation. This byte is cleared by the FPCP at the start of most operations; operations that
cannot generate any floating-point exceptions (the FMOVEM and FMOVE control register
instructions) do not clear this byte. This byte can be used by an exception handler to
determine which floating-point exception(s) caused a trap.
If a bit is set by the FPCP in the EXC byte and the corresponding bit in the ENABLE byte
is also set, an exception is signaled to the main processor. When a floating-point exception
is detected by the FPCP, the corresponding bit in the EXC byte is set, even if the trap for
15 14 13 12 11
10 8
' 1
I
9
I INEX2
I~F..XACT DECI~,'.At IHPUT
L'CEXACT OPERATIOH
DIVIDE BY
ZE~0
UNDERFIOW
0~'EF.:10W
0PEP~,ND EF,~0 R
BRANCH/SET ON U'IOF~E~D
Figure 2-6. MC68881/MC68882 FPSR Exception Status Byte
FREESCALE
2-6
MC68881/MC68882 USER'S MANUAL