cs 61C L10 Start.1Patterson Spring 99 ©UCBCS61CStarting a Program Lecture 10February 19, 1999Dave Patterson(http.cs.berkeley.edu/~patterson)www-inst.eecs.berkeley.edu/~cs61c/schedule.htmlcs 61C L10 Start.2Patterson Spring 99 ©UCBReview: New MIPS arithmetic instructions° Example Meaning Comments° mult $2,$3 Hi, Lo = $2 x $3 64-bit signed product° multu$2,$3 Hi, Lo = $2 x $3 64-bit unsigned product° div $2,$3 Lo = $2 ÷ $3, Lo = quotient, Hi = rem° divu $2,$3 Lo = $2 ÷ $3, Unsigned quotient, rem.° mfhi $1 $1 = Hi Used to get copy of Hi° mflo $1 $1 = Lo Used to get copy of Lo° add.s $0,$1,$2 $f0=$f1+$f2 Fl. Pt. Add (single)° add.d $0,$2,$4 $f0=$f2+$f4 Fl. Pt. Add (double)° sub.s $0,$1,$2 $f0=$f1-$f2 Fl. Pt. Subtract (single)° sub.d $0,$2,$4 $f0=$f2-$f4 Fl. Pt. Subtract (double)° mul.s $0,$1,$2 $f0=$f1x$f2 Fl. Pt. Multiply (single)° mul.d $0,$2,$4 $f0=$f2x$f4 Fl. Pt. Multiply (double)° div.s $0,$1,$2 $f0=$f1÷$f2 Fl. Pt. Divide (single)° div.d $0,$2,$4 $f0=$f2÷$f4 Fl. Pt. Divide (double)° c.X.s $0,$1 flag1= $f0 X $f1 Fl. Pt.Compare (single)° c.X.d $0,$2 flag1= $f0 X $f2 Fl. Pt.Compare (double) X is eq, lt, le; bc1t, bc1f tests flagcs 61C L10 Start.3Patterson Spring 99 ©UCBReview 2/2°IEEE 754 Floating Point standard:accuracy first class citizen°Multiply product 2n bits; Divide producesboth n-bit quotient and n-bit remainder°Computer numbers have limited size=> limited precision• underflow: too small for Fl. Pt.(bigger negative exponent than can represent)• overflow: too big for Fl. Pt. or integer (bigger positive exponent than can represent,or bigger integer than fits in word)• Programmers beware!cs 61C L10 Start.4Patterson Spring 99 ©UCBOutline°Floating Point Questions and Answers°Compiling, Assembling a Program°Administrivia, “Computers in the News”°Linking, Loading a Program°An Example°Conclusioncs 61C L10 Start.5Patterson Spring 99 ©UCBFloating Point Questions: Negative 0?°What is result of this program?main() {float i,j;i = 1.0; j = 0.0;printf("%3.1f\n",i/j);printf("%3.1f\n",-i/j);printf("%3.1f\n",j/(-i/j));if (j/(-i/j) == 0.0)printf("0.0 == -0.0\n");else printf("0.0 != -0.0\n");printf("%3.1f\n",i/j-i/j);printf("%3.1f\n",(i/j-i/j)+i);}°Output:Inf-Inf-0.00.0 == -0.0NaNNaNcs 61C L10 Start.6Patterson Spring 99 ©UCBBig Idea: Levels of Abstaction (Unix/DOS)C program: foo.c/foo.txtAssembly program: foo.s/ foo.asmExecutable(mach lang pgm): a.out/foo.exeCompilerAssemblerLinkerLoaderMemoryObject(mach lang module): foo.o/foo.objlib.o/lib.objcs 61C L10 Start.7Patterson Spring 99 ©UCBAssembler°Follow Directions°Replace Pseudoinstructions°Find list of labels, addresses°Produce machine language°Creates Object Filecs 61C L10 Start.8Patterson Spring 99 ©UCBExample Assembly Program: Directives.text.align 2.globl mainmain:subu $sp,$sp,32sw $ra, 20($sp)sd $a0, 32($sp)sw $0, 24($sp)sw $0, 28($sp)loop:lw $t6, 28($sp)mul $t7, $t6,$t6lw $t8, 24($sp)addu $t9,$t8,$t7sw $t9, 24($sp) addu $t0, $t6, 1sw $t0, 28($sp)ble $t0,100, loopla $a0, strlw $a1, 24($sp)jal printfmove $v0, $0lw $ra, 20($sp)addiu $sp,$sp,32j $ra.data.align 0str:.asciiz "The sumfrom 0 .. 100 is%d\n"cs 61C L10 Start.9Patterson Spring 99 ©UCBAssembler Directives (p. A-51 to A-53)°Tell assembler how to translate programbut do not produce machine instructions .text (addr): Subsequent items put inuser text segment (starting at addr) .align n: Align the next data on a 2n byteboundary; align 2 ⇒ next word boundary .globl sym: declares sym global and canbe referenced from other files .data (addr): Subsequent items put inuser data segment (starting at addr) .asciiz str: Store the string str inmemory and null-terminate itcs 61C L10 Start.10Patterson Spring 99 ©UCBExample Assembly Program: PseudoInstr.text.align 2.globl mainmain:subu $sp,$sp,32sw $ra, 20($sp)sd $a0, 32($sp)sw $0, 24($sp)sw $0, 28($sp)loop:lw $t6, 28($sp)mul $t7, $t6,$t6lw $t8, 24($sp)addu $t9,$t8,$t7sw $t9, 24($sp) addu $t0, $t6, 1sw $t0, 28($sp)ble $t0,100,loopla $a0, strlw $a1, 24($sp)jal printfmove $v0, $0lw $ra, 20($sp)addiu $sp,$sp, 32j $ra.data.align 0str:.asciiz "The sumfrom 0 .. 100 is%d\n"cs 61C L10 Start.11Patterson Spring 99 ©UCBPseudoinstruction replacements°Asm. treats common variations of machinelanguage instructions as if real instructions¥subu $sp,$sp,32 addiu $sp,$sp,-32¥sd $a0, 32($sp) sw $a0, 32($sp)sw $a1, 36($sp)¥mul $t7,$t6,$t6 mul $t6,$t6mflo $t7¥addu $t0,$t6,1 addiu $t0,$t6,1¥ble $t0,100,loop slti $at,$t0,101bne $at,$0,loop¥la $a0, str lui $at,left(str) ori $a0,$at,right(str)¥move $v0, $0 add $v0,$0,$0cs 61C L10 Start.12Patterson Spring 99 ©UCBExample Assembly Program: Labels.text.align 2.globl mainmain:subu $sp,$sp,32sw $ra, 20($sp)sd $a0, 32($sp)sw $0, 24($sp)sw $0, 28($sp)loop:lw $t6, 28($sp)mul $t7, $t6,$t6lw $t8, 24($sp)addu $t9,$t8,$t7sw $t9, 24($sp) addu $t0, $t6, 1sw $t0, 28($sp)ble $t0,100, loopla $a0, strlw $a1, 24($sp)jal printfmove $v0, $0lw $ra, 20($sp)addiu $sp,$sp,32j $ra.data.align 0str:.asciiz "The sumfrom 0 .. 100 is%d\n"cs 61C L10 Start.13Patterson Spring 99 ©UCBAddresses°Main job of Assembler:1) Find list of labels and their addresses2) Produce machine language°Puts label and memory address of thatinstruction in Symbol Table°Can use a name before it is defined;forward reference e.g., str in example• Note: Must declare before use in C°Uses Symbol Table in 2nd pass toproduce machine code, includingaddressescs 61C L10 Start.14Patterson Spring 99 ©UCBAdministrivia°Readings: (3.9) A.2, A.3, A.4, 3.10, 3.11°5th homework: Due 2/24 7PM• Exercises 4.21, 4.25, 4.28°3rd Project/5th Lab: MIPS Simulator Due Wed. 3/3 7PM; deadline Thurs 8AM• Twice / semester 24-hour extension• Everything (but midterm) may be done inpairs now°Solutions : ~cs61c/solutions directory.Access it using cs61c account. Not www!°Midterm conflict time: Mon 3/15 6-9PMcs 61C L10 Start.15Patterson Spring 99 ©UCB“Computers in the News”°“Microsoft Denies Rumors That It Is Craftinga Language Like Java”, NY Times, 2/15/99• “Microsoft Corp. is playing down a report in‘PC Week’ that it has been briefing softwaredevelopers on a new programming language(code-named ‘Cool’) that would be similar toSun's Java software.” [Java SW not binaries]• “.... Cross platform means that a developer canwrite one version of a program in Java, whichcan then run on Windows, Macintosh, Unix andother software
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