CVT Instruction

Purpose:

To convert a Signed quantity to a different data type.

Format:

opcode src.rx, dst.wy

Operation:

dst <- converted src;

Condition
Codes:

N <- dst LSS 0;
Z <- dst EQL 0;
V <- {src cannot be represented in dst};
C <- 0;

Exceptions:

Integer Overflow;
Floating Point Overflow
Reserved Operand (Floating Point)

Opcodes:

99	CVTBW	Convert Byte to Word	98	CVTBL	Convert Byte to Long
4C	CVTBF	Convert Byte to Float	6C	CVTBD	Convert Byte to Double
33	CVTWB	Convert Word to Byte	32	CVTWL	Convert Word to Long
4D	CVTWF	Convert Word to Float	6D	CVTWD	Convert Word to Double
F6	CVTLB	Convert Long to Byte	F7	CVTLW	Convert Long to Word
4E	CVTLF	Convert Long to Float	6E	CVTLD	Convert Long to Double
48	CVTFB	Convert Float to Byte	49	CVTFW	Convert Float to Word
4A	CVTFL	Convert Float to Long	4B	CVTRFL	Convert Rounded Float to Long
56	CVTFD	Convert Float to Double	68	CVTDB	Convert Double to Byte
69	CVTDW	Convert Double to Word	6A	CVTDL	Convert Double to Long
6B	CVTRDL	Convert Double Rounded to Long	76	CVTDF	Convert Double to Float

Description:

The source operand is convert to the data type of the destination operand and the destination operand is replaced by the result. The source operand is unaffected.

For integer format, conversion of a shorter data type to a longer data type is done by sign extension. A conversion of a longer data type to a shorter data type is done by truncation of the most significant bit.

For floating format, teh conversions are as follows:

CVTBF exact CVTFB truncated
CVTBD exact CVTDB truncated
CVTWF exact CVTFW truncated
CVTWD exact CVTDW truncated
CVTLF rounded CVTFL truncated
CVTLD exact CVTDL truncated
CVTFD exact CVTDF rounded
CVTRFL rounded CVTRDL rounded

Notes:

1.: Integer overflow occurs if any trucated bits of the source operand are not equal to the sign bit of the destination operand.
2.: Only converts with an integer destination operand can result in an integer overflow. On integer overflow, the destination operand is replaced by the low order bits of the true result.
3.: Only CVTDF can result in floating overflow. On floating overflow, the destination operand is replaced by an operand of all 0 bits except for a sign bit of 1 (a reserved operand). N <- 1; Z &lf- 0; V <-1; and C <- 0.
4.: Only converts with a floating point source operand can result in a reserved operand fault. On a reserved operand fault, the destination operand is unaffected and the condition codes are unpredictable.