HP OpenVMS Systems Documentation

Subtract

Format

2operand: opcode sub.rx, dif.mx

3operand: opcode sub.rx, min.rx, dif.wx

Condition Codes

Exceptions

floating overflow
floating underflow
reserved operand

Opcodes

Description

In 2 operand format, the subtrahend operand is subtracted from the difference operand, and the difference is replaced by the rounded result. In 3 operand format, the subtrahend operand is subtracted from the minuend operand, and the difference operand is replaced by the rounded result.

Notes

1. On a reserved operand fault, the difference operand is unaffected, and the condition codes are UNPREDICTABLE.
2. On floating underflow, if FU is set, a fault occurs. Zero is stored as the result of floating underflow only if FU is clear. On a floating underflow fault, the difference operand is unaffected. If FU is clear, the difference operand is replaced by zero, and no exception occurs.
3. On floating overflow, the instruction faults, the difference operand is unaffected, and the condition codes are UNPREDICTABLE.

Test

Format

opcode src.rx

Condition Codes

Exceptions

reserved operand

Opcodes

Description

The condition codes are affected according to the value of the source operand.

Notes

1. TSTx src is equivalent to CMPx src, #0, but is 5 (F_floating) or 9 (D_floating or G_floating) or 17 (H_floating) bytes shorter.
2. On a reserved operand fault, the condition codes are UNPREDICTABLE.

9.2.9 Character String Instructions

1. An unsigned word operand that specifies the length of the character string in bytes.
2. The address of the lowest-addressed byte of the character string. This is specified by a byte operand of address access type.

Each of the character string instructions uses general registers R0 to R1, R0 to R3, or R0 to R5 to contain a control block that maintains updated addresses and state during the execution of the instruction. At completion, these registers are available to software to use as string specification operands for a subsequent instruction on a contiguous character string. During the execution of the instructions, pending interrupt conditions are tested. If any conditions are found, the control block is updated, a first-part-done bit is set in the processor status longword (PSL), and the instruction is interrupted (refer to Appendix E). After the interruption, the instruction resumes transparently. The format of the control block is as follows:

The fields LENGTH 1, LENGTH 2 (if required), and LENGTH 3 (if required) contain the number of bytes remaining to be processed in the first, second, and third string operands, respectively. The fields ADDRESS 1, ADDRESS 2 (if required), and ADDRESS 3 (if required) contain the address of the next byte to be processed in the first, second, and third string operands, respectively.

Memory access faults do not occur when a zero-length string is specified because no memory reference occurs.

The following instructions are described in this section.

Compare Characters

Format

3operand: opcode len.rw, src1addr.ab,

src2addr.ab 5operand: opcode src1len.rw, src1addr.ab, fill.rb,

src2len.rw, src2addr.ab

Condition Codes

Exceptions

None.

Opcodes

Description

In 3 operand format, the bytes of string1 specified by the length and address1 operands are compared with the bytes of string2 specified by the length and address2 operands. Comparison proceeds until inequality is detected or all the bytes of the strings have been examined. Condition codes are affected by the result of the last byte comparison. In 5 operand format, the bytes of the string1 operand specified by the length1 and address1 operands are compared with the bytes of the string2 operand specified by the length2 and address2 operands. If one string is longer than the other, the shorter string is conceptually extended to the length of the longer by appending (at higher addresses) bytes equal to the fill operand. Comparison proceeds until inequality is detected or all the bytes of the strings have been examined. Condition codes are affected by the result of the last byte comparison. For either CMPC3 or CMPC5, two zero-length strings compare equal (that is, Z is set and N, V, and C are cleared).

Notes

1. After execution of CMPC3:

   R0 =	Number of bytes remaining in string1 (including byte that terminated comparison); R0 is zero only if strings are equal
   R1 =	Address of the byte in string1 that terminated comparison; if strings are equal, address of 1 byte beyond string1
   R2 =	R0
   R3 =	Address of the byte in string2 that terminated comparison; if strings are equal, address of 1 byte beyond string2

2. After execution of CMPC5:

   R0 =	Number of bytes remaining in string1 (including byte that terminated comparison); R0 is zero only if string1 and string2 are of equal length and equal or string1 was exhausted before comparison terminated
   R1 =	Address of the byte in string1 that terminated comparison; if comparison did not terminate before string1 exhausted, address of 1 byte beyond string1
   R2 =	Number of bytes remaining in string2 (including byte that terminated comparison); R2 is zero only if string2 and string1 are of equal length or string2 was exhausted before comparison terminated
   R3 =	Address of the byte in string2 that terminated comparison; if comparison did not terminate before string2 was exhausted, address of 1 byte beyond string2

3. If both strings have zero length, condition code Z is set and N, V, and C are cleared just as in the case of two equal strings.

Locate Character

Format

opcode char.rb, len.rw, addr.ab

Condition Codes

Exceptions

None.

Opcodes

Description

The character operand is compared with the bytes of the string specified by the length and address operands. Comparison continues until equality is detected or all bytes of the string have been compared. If equality is detected, the condition code Z-bit is cleared; otherwise, the Z-bit is set.

Notes

1. After execution:

   R0 =	Number of bytes remaining in the string (including located one) if byte located; otherwise, zero
   R1 =	Address of the byte located if byte located; otherwise, address of 1 byte beyond the string

2. If the string has zero length, condition code Z is set just as though each byte of the entire string were unequal to character.

Match Characters

Format

opcode objlen.rw, objaddr.ab, srclen.rw, srcaddr.ab

Condition Codes

Exceptions

None.

Opcodes

Description

The source string specified by the source length and source address operands is searched for a substring that matches the object string specified by the object length and object address operands. If the substring is found, the condition code Z-bit is set; otherwise, it is cleared.

Notes

1. After execution:

   R0 =	If a match occurred, zero; otherwise, the number of bytes in the object string
   R1 =	If a match occurred, the address of 1 byte beyond the object string; that is, objaddr + objlen; otherwise, the address of the object string
   R2 =	If a match occurred, the number of bytes remaining in the source string; otherwise, zero
   R3 =	If a match occurred, the address of 1 byte beyond the last byte matched; otherwise, the address of 1 byte beyond the source string; that is, srcaddr + srclen

   
   For zero-length source and object strings, R3 and R1 contain the source and object addresses, respectively.
2. If both strings have zero length, or if the object string has zero length, condition code Z is set, and registers R0 to R3 are left just as though the substring were found.
3. If the source string has zero length and the object string has nonzero length, condition code Z is cleared, and registers R0 to R3 are left just as though the substring were not found.

Move Character

Format

3operand: opcode len.rw, srcaddr.ab, dstaddr.ab

5operand: opcode srclen.rw, srcaddr.ab, fill.rb,

dstlen.rw, dstaddr.ab

Condition Codes

Exceptions

None.

Opcodes

Description

In 3 operand format, the destination string specified by the length and destination address operands is replaced by the source string specified by the length and source address operands. In 5 operand format, the destination string specified by the destination length and destination address operands is replaced by the source string specified by the source length and source address operands. If the destination string is longer than the source string, the highest-addressed bytes of the destination are replaced by the fill operand. If the destination string is shorter than the source string, the highest-addressed bytes of the source string are not moved. The operation of the instruction is such that overlap of the source and destination strings does not affect the result.

Notes

1. After execution of MOVC3:

   R0 =	0
   R1 =	Address of 1 byte beyond the source string
   R2 =	0
   R3 =	Address of 1 byte beyond the destination string
   R4 =	0
   R5 =	0

2. After execution of MOVC5:

   R0 =	Number of unmoved bytes remaining in source string. R0 is nonzero only if source string is longer than destination string
   R1 =	Address of 1 byte beyond last byte in source that was moved
   R2 =	0
   R3 =	Address of 1 byte beyond the destination string
   R4 =	0
   R5 =	0

3. MOVC3 is the preferred way to copy one block of memory to another.
4. MOVC5 with a zero source length operand is the preferred way to fill a block of memory with the fill character.

Move Translated Characters

Format

opcode srclen.rw, srcaddr.ab, fill.rb, tbladdr.ab,

dstlen.rw, dstaddr.ab

Condition Codes

Exceptions

None.

Opcodes

Description

The source string specified by the source length and source address operands is translated. It replaces the destination string specified by the destination length and destination address operands. Translation is accomplished by using each byte of the source string as an index into a 256-byte table whose first entry (entry number 0) address is specified by the table address operand. The byte selected replaces the byte of the destination string. If the destination string is longer than the source string, the highest-addressed bytes of the destination string are replaced by the fill operand. If the destination string is shorter than the source string, the highest-addressed bytes of the source string are not translated and moved. The operation of the instruction is such that overlap of the source and destination strings does not affect the result.

If the destination string overlaps the translation table, the destination string is UNPREDICTABLE.

Notes

1. After execution:

   R0 =	Number of untranslated bytes remaining in source string; R0 is nonzero only if source string is longer than destination string
   R1 =	Address of 1 byte beyond the last byte in source string that was translated
   R2 =	0
   R3 =	Address of the translation table
   R4 =	0
   R5 =	Address of 1 byte beyond the destination string