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| Table 3.21 Length (by class). |
| | Commercial | | | I (a) | Move characters | 32.6B |  |
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(b) |
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| Move decimal | | | |
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operand 1 |
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| 4.2B | | |
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operand 2 |
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| 3.3B | | II | Test, compare, logical | | | |
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(as specified) |
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| 3.5B | | |
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(as executed) |
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| 2.0B | | III | Decimal arithmetic | | | Operand 1 | 4.2B | | Operand 2 | 2.5B |
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| Table 3.22 Frequency of variable operand length instructions in R/M or R+M. | | | | | | I (a) | Move character | | | |
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(b) |
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| Move decimal | | | | II | Test, compare, logical (character) | | | | III | Decimal arithmetic | | |
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incident rightmost bytes. Table 3.21 indicates operand lengths from the decimal instructions in a Cobol object mix. |
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There are basically six generic decimal instructions (all MM format): Pack (PACK), Unpack (UNPK), Add (ADD.P), Subtract (SUB.P), Multiply (MPY.P), and Divide (DIV.P). The Pack instruction takes the second operand and translates it from character or digit-per-byte representation to the packed two-digit-per-byte representation used in arithmetic processing. Unpack is the complementary operation. The four basic arithmetic operations follow expected conventions by using the format first operand OP second operand ® first operand, and by keeping all operands in memory with length not exceeding 16 bytes. |
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Length of String Operands Character and decimal operands have variable length (up to 256 bytes for character operands). Since execution time is almost always a function of operand length, the distribution of these operands is important. For execution purposes, character and decimal operations fall into one of three distinct types: |
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1. One source operand (of variable size) and a separate result operand (of variable size). Included here is MOVE.C. Certain decimal instructions form a separate sub-class (ZMOVE.P, PACK, and UNPK). |
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