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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;
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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TODAY’S FOCUS Shift Instructions
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
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
Logical Operators

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## This note was uploaded on 12/27/2011 for the course CMPSC 64 taught by Professor Zheng during the Fall '09 term at UCSB.

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

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