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Arithmetic and Logic Instructions

Arithmetic and Logic Instructions. A Course in Microprocessor Electrical Engineering Department University of Indonesia. Addition-Subtraction-Comparison. Whenever arithmetic and logic instruction execute, the contents of the flag register change Addition

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Arithmetic and Logic Instructions

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  1. Arithmetic and Logic Instructions A Course in Microprocessor Electrical Engineering Department University of Indonesia

  2. Addition-Subtraction-Comparison Whenever arithmetic and logic instruction execute, the contents of the flag register change • Addition Table 5.1 illustrates the addressing modes available to the ADD instructions • Register Addition • Example 5.1 show a sample of register addition • Immediate Addition • Example 5.2 shows 8-bit immediate addition example

  3. Addition-Subtraction-Comparison (cont’d) • Memory-to-Register Addition • Example 5.3 adds two consecutive bytes of data • Array Addition • Example 5.4 shows a procedure that adds the contents of array elements 3, 5, and 7 • Example 5.5 shows the scaled-index form of addressing to add elements 3, 5, and 7 of an area of memory called ARRAY • Increment Addition • Examples 5.6 modifies example 5.3 to use the increment instruction for addressing NUMB and NUMB+1 (see also Table 5.2)

  4. Addition-Subtraction-Comparison (cont’d) • Addition-with-Carry • Table 5.3 lists several add-with-carry instruction • Figure 5.1 illustrates the addition • Ex. 5.7 and Ex. 5.8 show the short program • Subtraction • Table 5.4 shows addressing modes for the subtraction instruction • Register Subtraction • Example 5.9 • Immediate Subtraction • Example 5.10

  5. Addition-Subtraction-Comparison (cont’d) • Decrement Subtraction • It subtracs a 1 from a register or the contents of a memory location (see Table 5.5) • Subtract-with-Borrow • It functions as a regular subtraction, except that the carry flag (C) which holds the borrow, also subtracts from the difference (see Table 5.6 & Ex. 5.11) • Comparison • The comparison instruction (CMP) is a subtraction that changes only the flag bits • See Table 5.7 and Example 5.12

  6. Multiplication and Division • Only modern p contain multiplication and division instructions • Multiplication • multiplication (bytes, words, or doublewords) can be signed integer (IMUL) or unsigned (MUL) • 8-bit Multiplication • The multiplicant is always in the register AL • See Table 5.8 and Example 5.13 • 16-bit Multiplication • AX contains the multiplicand and the product appears in DX-AX

  7. Multiplication and Division (cont’d) • 32-bit Muliplication • The contents of EAX are multiplied by the operand specified with the instruction • The product (64-bits wide) is found in EDX-EAX where EAX contains the LS32B (see Table 5.10) • Division • None of the flag bits change predictably; i.e., a division can result is two different types of error: • an attempt to divide by zero • a divide overflow (see the 3rd paragraph in p.157) • In both cases, the p generates an interrupt if a divide error occurs

  8. Multiplication and Division (cont’d) • 8-bit Division • The AX register stores the dividend • After the division, AL contains the quotient and AH contains a whole number remainder • See Table 5.11, Example 5.14 & Example 5.15 • 16-bit Division • Instead of dividing into AX, the 16-bit number is divided into DX-AX, a 32-bit dividend • The qutient appears in AX and the remainder in DX after a 16-bit division • See Table 5.12 and Example 5.16

  9. Multiplication and Division (cont’d) • 32-bit Division • The 64-bit contents of EDX-EAX are divided by the operand specified by the instruction, leaving a 32-bit quotient in EAX and a 32-bit remainder in EDX • See Table 5.13 • The Remainder • After a division, the remainder could be use to round the result or dropped to truncate the result or conver-ted to a fractional remainder • Study Example 5.17 and Example 5.18

  10. BCD and ASCII Arithmetic • BCD Arithmetic • p allows arithmetic manipulation of both BCD and ASCII • DAA (Decimal Adjust After Addition) Instruction • It follows the ADD or ADC instruction to adjust the result into a BCD result (Ex. 5.19) • DAS (Decimal Adjust After Subtraction) Instruction • It functions as does the DAA, except that it follows a subtraction instead of an addition (Ex. 5.20)

  11. BCD and ASCII Arithmetic (cont’d) • ASCII Arithmetic • AAA (ASCII Adjust After Addition) • Example 5.21 • AAD (ASCII Adjust Before Division) • Example 5.22 • AAM (ASCII Adjust After Multiplication) • Example 5.23, Example 5.24, Example 5.25 • AAS (ASCII Adjust After Subtraction) • Adjust the AX register after an ASCII subtraction

  12. Basic Logic Instruction • Logic operations provide binary bit control in low-level software; allow bits to be set, cleared, or complemented • AND • Performs logical multiplication as depicted by the truth table in Fig.5.3 and Fig. 5.4 • See also Ex. 5.26 and Table 5.14 • OR • Performs logical addition as depicted in Fig. 5.5 and Ex. 5.27 and Fig. 5.6 and Table 5.15 • X-OR • Study Fig. 5.7, Table 5.16 and Ex 5.28

  13. Basic Logic Instruction (cont’d) • Test and Bit Test Instruction • Test instruction performs the AND operation; the differece is that the AND instruction changes the destination operand, while the TEST does not • Test instruction affects only the flag (Table 5.17 and Example 5.29) • Bit Test instruction tests single bit position (Table 5.18 and Example 5.30 • NOT and NEG • NOT performs logical inversion (1’s complement) and NEG performs arithmetic sign inversion (2’s complement)

  14. Shift and Rotate • Shift and Rotate instructions manipulate binary numbers at the binary bit level • Shifts and Rotates find their most common application in low-level software used to control I/O devices • Shifts • Shifts position or move numbers to the left or right within a register or memory location • Shifts also perform simple arithmetic such as multiplication by powers of 2+n (left shift) and division by powers of 2-n (right shift) • Study fig. 5.9, Table 5.20, Examples 5.31 & 5.32

  15. Shift and Rotate (cont’d) • Rotate • Rotates position binary data by rotating the infromation in a register or memory location either from one end to another or through the carry flag • Rotates are often used to shift wide numbers to the left or right • Study Fig. 5.10, Table 5.21, Example 5.33 • Bit Scan Instructions • BSF (bit scan forward) and BSR (bit scan reverse) scan through a number searching for the first 1-bit encountered

  16. String Comparisons • It is very powerful because allows to manipulate large blocks of data with relative ease • SCAS • SCAS compares the AL register with a byte block of memory (SCASB), the AX register with a word block of memory (SCASW), or the EAX register with a doubleword block of memory (SCASD) • study Example 5.34 and Example 5.35 • CMPS • It always compares two sections of memory data as bytes (CMPSB), word (CMPSW), or doubleword (CMPSD); Study Example 5.36

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