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lecture6 - Lecture 6 Decision Shift I/O Instructions so far...

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Lecture 6 Decision + Shift + I/O
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Instructions so far MIPS C Program add, sub, addi, multi, div a=b+c, a=b-c, a=b+10, a=b*c, a=b/c lw $t0,12($s0) sw $t0, 12($s0) t= A[3] A[3]=t beq $s0, $s1, L1 bne $s0, $s1, L1 If (a==b) go to L1 If (a!=b) go to L1 j L1 (unconditional branch) goto L1 slt reg1,reg2,reg3 if (reg2 < reg3) reg1 = 1; else reg1 = 0;
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Optional Individual Submission for Today’s Quiz Turnin under quiz2 In the program, include your name/perm number By 11:59PM Tonight
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T O D A Y ’ S F O C U S Shift Instructions
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Bitwise Operations Up until now, we’ve done arithmetic (add, sub,addi ), memory access (lw and sw), and branches and jumps. All of these instructions view contents of register as a single quantity (such as a signed or unsigned integer) New Perspective : View contents of register as 32 individual bits rather than as a single 32-bit number
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Bitwise Operations Since registers are composed of 32 bits, we may want to access individual bits (or groups of bits) rather than the whole. Introduce two new classes of instructions: Logical Operators Shift Instructions
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Logical Operators Two basic logical operators: AND: outputs 1 only if both inputs are 1 OR: outputs 1 if at least one input is 1 In general, can define them to accept >2 inputs, but in the case of MIPS assembly, both of these accept exactly 2 inputs and produce 1 output Again, rigid syntax, simpler hardware
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Logical Operators Truth Table: standard table listing all possible combinations of inputs and resultant output for each Truth Table for AND and OR A B A AND B A OR B 0 0 0 1 1 0 1 1 0 1 1 1 0 0 0 1
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Logical Operators
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