This web page examines data conversion instructions in assembly language. Specific examples of instructions from various processors are used to illustrate the general nature of assembly language.
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Data conversion instructions change data from one format to another.
A sign extension operation takes a small value and sign extends it to a larger storage format (such as byte to word).
A type conversion operation changes data from one format to another (such as signed two’s complement integer into binary coded decimal).
EXT Sign Extend; Motorola 680x0, Motorola 68300; sign extends a byte (8 bits) in a data register to a word (16 bits) or sign extends a word (16 bits) in a data register to a longword (32 bits); sets or clears flags
CVT Convert; DEC VAX; converts a signed quantity to a different signed data type, source and destination in register or memory, special rounded versions for certain floating conversions; sets or clears flags
CVTBW Convert Byte to Word; sign extend
CVTBL Convert Byte to Long; sign extend
CVTWB Convert Word to Byte; truncated
CVTWL Convert Word to Long; sign extend
CVTLB Convert Long to Byte; truncated
CVTLW Convert Long to Word; truncated
CVTBF Convert Byte to Floating; exact
CVTBD Convert Byte to Double float; exact
CVTWF Convert Word to Floating; exact
CVTWD Convert Word to Double float; exact
CVTLF Convert Long to Floating; rounded
CVTLD Convert Long to Double float; exact
CVTFB Convert Floating to Byte; truncated
CVTDB Convert Double float to Byte; truncated
CVTFW Convert Floating to Word; truncated
CVTDW Convert Double float to Word; truncated
CVTFL Convert Floating to Long; truncated
CVTRFL Convert Rounded Floating to Long; rounded
CVTDL Convert Double float to Long; truncated
CVTRDL Convert Rounded Double float to Long; rounded
CVTFD Convert Floating to Double float; exact
CVTDF Convert Double float to Floating; rounded
CBW Convert Byte to Word; Intel 80x86; sign extends a byte (8 bits) in register AL to create a word (16 bits) in the AX register; does not affect flags
CWD Convert Word to Doubleword; Intel 80x86; sign extends a word (16 bits) in register AX throughout the DX register to create a doubleword (32 bits); does not affect flags
CWDE Convert Word to Doubleword Extended; Intel 80386; sign extends a word (16 bits) in register AX to create a doubleword (32 bits) in the EAX register; does not affect flags
CDQ Convert Doubleword to Quadword; Intel 80386; sign extends a doubleword (32 bits) in register EAX to create a quadword (64 bits) in the EDX register; does not affect flags
EXTB Sign Extend Byte; Motorola 680x0, Motorola 68300; sign extends a byte (8 bits) in a data register to a longword (32 bits); sets or clears flags
MOVSX Move with Sign Extension; Intel 80x86; moves data from a register or memory to a register, with a sign extension (conversion to larger binary integer: byte to word, byte to doubleword, or word to doubleword); does not affect flags
MOVZX Move with Zero Extension; Intel 80x86; moves data from a register or memory to a register, with a zero extension (conversion to larger binary integer: byte to word, byte to doubleword, or word to doubleword); does not affect flags
MOVZ Move Zero Extended; DEC VAX; converts an unsigned integer to a larger unsigned integer, source and destination in register or memory (MOVZBW Byte to Word, MOVZBL Byte to Long, MOVZWL Word to Long); sets or clears flags
NUM Convert to Numeric; MIX; converts byte encoded character code (MIX character code) in A-register/X-register pair to numeric data in the A-register (accumulator), does not change sign, overflow possible
CHAR Convert to Characters; MIX; converts numeric data in the A-register (accumulator) into byte encoded character code (MIX character code) in A-register/X-register pair, does not change signs
PACK Pack; Motorola 680x0; converts byte encoded numeric data (such as ASCII or EBCDIC characters) into binary coded decimals using an adjustment field ($3030 for ASCII, $F0F0 for EBCDIC), either from data register to data register or memory location to memory location with predecrement of address pointers; does not modify flags
UNPK Unpack; Motorola 680x0; converts binary coded decimals into byte encoded numeric data (such as ASCII or EBCDIC characters) using an adjustment field ($3030 for ASCII, $F0F0 for EBCDIC), either from data register to data register or memory location to memory location with predecrement of address pointers; does not modify flags
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