216 lines
9.1 KiB
Markdown
216 lines
9.1 KiB
Markdown
------------------------ --------------------------------- --------------------
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[Previous](15-03.html) [Table of Contents](index.html) [Next](16-01.html)
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------------------------ --------------------------------- --------------------
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**LISTING 15.7 L15-7.ASM**
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; C near-callable assembly function for inserting a new node in a
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; linked list sorted by ascending order of the Value field. The list
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; is circular; that is, it has a dummy node as both the head and the
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; tail of the list. The dummy node is a sentinel, containing the
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; largest possible Value field setting. Tested with TASM.
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MAX_TEXT_LENGTH equ 100 ;longest allowed Text field
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SENTINEL equ 32767 ;largest possible Value field
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LinkNode struc
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NextNode dw ?
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Value dw ?
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Text db MAX_TEXT_LENGTH+1 dup(?)
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;*** Any number of additional data fields may by present ***
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LinkNode ends
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.model small
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.code
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; Inserts the specified node into a ascending-value-sorted linked
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; list, such that value-sorting is maintained. Returns a pointer to
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; the node after which the new node is inserted.
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; C near-callable as:
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; struct LinkNode *InsertNodeSorted(struct LinkNode *HeadOfListNode,
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; struct LinkNode *NodeToInsert)
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parms struc
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dw 2 dup (?) ;pushed return address & BP
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HeadOfListNode dw ? ;pointer to head node of list
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NodeToInsert dw ? ;pointer to node to insert
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parms ends
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public _InsertNodeSorted
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_InsertNodeSorted proc near
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push bp
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mov bp,sp ;point to stack frame
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push si ;preserve register vars
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push di
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mov si,[bp].NodeToInsert ;point to node to insert
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mov ax,[si].Value ;search value
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mov di,[bp].HeadOfListNode ;point to linked list in
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; which to insert
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SearchLoop:
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mov bx,di ;advance to the next node
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mov di,[bx].NextNode ;point to following node
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cmp [di].Value,ax ;is the following node's
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; value less than the value
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; from the node to insert?
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jl SearchLoop ;yes, so continue searching
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;no, so we have found our
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; insert point
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mov ax,[bx].NextNode ;link the new node between
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mov [si].NextNode,ax ; the current node and the
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mov [bx].NextNode,si ; following node
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mov ax,bx ;return pointer to node
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; after which we inserted
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pop di ;restore register vars
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pop si
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pop bp
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ret
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_InsertNodeSorted endp
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end
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**LISTING 15.8 L15-8.C**
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/* Sample linked list program. Tested with Borland C++. */
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#include <stdlib.h>
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#include <stdio.h>
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#include <conio.h>
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#include <ctype.h>
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#include <string.h>
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#include “llist.h”
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void main()
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{ int Done = 0, Char, TempValue;
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struct LinkNode *TempPtr, *ListPtr, *TempPtr2;
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char TempBuffer[MAX_TEXT_LENGTH+3];
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if ((ListPtr = InitLinkedList()) == NULL) {
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printf(“Out of memory\n”);
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exit(1);
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}
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while (!Done) {
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printf(“\nA=add; D=delete; F=find; L=list all; Q=quit\n>”);
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Char = toupper(getche());
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printf(“\n”);
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switch (Char) {
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case 'A': /* add a node */
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if ((TempPtr = malloc(sizeof(struct LinkNode))) == NULL)
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{
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printf(“Out of memory\n );
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exit(1);
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}
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printf(“Node value: ”);
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scanf(“%d”, &TempPtr->Value);
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if ((FindNodeBeforeValue(ListPtr,TempPtr->Value))!=NULL)
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{ printf(“*** value already in list; try again ***\n”);
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free(TempPtr);
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} else {printf(“Node text: ”);
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TempBuffer[0] = MAX_TEXT_LENGTH;
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cgets(TempBuffer);
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strcpy(TempPtr->Text, &TempBuffer[2]);
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InsertNodeSorted(ListPtr, TempPtr);
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printf(“\n”);
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}
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break;
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case 'D': /* delete a node */
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printf(“Value field of node to delete: ”);
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scanf(“%d”, &TempValue);
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if ((TempPtr = FindNodeBeforeValue(ListPtr, TempValue))
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!= NULL) {
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TempPtr2 = TempPtr->NextNode; /* -> node to delete */
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DeleteNodeAfter(TempPtr); /* delete it */
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free(TempPtr2); /* free its memory */
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} else {
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printf(“*** no such value field in list ***\n”)
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break;
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case 'F': /* find a node */
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printf(“Value field of node to find: ”);
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scanf(“%d”, &TempValue);
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if ((TempPtr = FindNodeBeforeValue(ListPtr, TempValue))
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!= NULL)
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printf(“Value: %d\nText: %s\n”,
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TempPtr->NextNode->Value, TempPtr->NextNode->Text);
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else
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printf(“*** no such value field in list ***\n”);
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break;
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case 'L': /* list all nodes */
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TempPtr = ListPtr->NextNode; /* point to first node */
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if (TempPtr == ListPtr) { /* empty if at sentinel */
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printf(“*** List is empty ***\n”);
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} else {
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do {printf(“Value: %d\n Text: %s\n”, TempPtr->Value,
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TempPtr->Text);
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TempPtr = TempPtr->NextNode;
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} while (TempPtr != ListPtr);
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}
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break;
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case 'Q':
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Done = 1;
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break;
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default:
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break;
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}
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}
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}
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### Hi/Lo in 24 Bytes {#Heading6}
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In one of my *PC TECHNIQUES* “Pushing the Envelope” columns, I passed
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along one of David Stafford’s fiendish programming puzzles: Write a
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C-callable function to find the greatest or smallest unsigned **int**.
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Not a big deal—except that David had *already* done it in 24 bytes, so
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the challenge was to do it in 24 bytes or less.
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Such routines soon began coming at me from all angles. However (and I
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hate to say this because some of my correspondents were *very* pleased
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with the thought that they had bested David), no one has yet met the
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challenge—because most of you folks missed a key point. When David said,
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“Write a function to find the greatest or smallest unsigned **int** in
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24 bytes or less,” he meant, “Write the **hi** and the **lo** functions
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in 24 bytes or less—*combined*.”
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Oh.
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Yes, a 24-byte hi/lo function is possible, anatomically improbable as it
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might seem. Which I guess goes to show that when one of David’s puzzles
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seems less than impossible, odds are you’re missing something. Listing
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15.9 is David’s 24-byte solution, from which a lot may be learned if one
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reads closely enough.
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**LISTING 15.9 L15-9.ASM**
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; Find the greatest or smallest unsigned int.
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; C callable (small model); 24 bytes.
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; By David Stafford.
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; unsigned hi( int num, unsigned a[] );
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; unsigned lo( int num, unsigned a[] );
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public _hi, _lo
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_hi: db 0b9h ;mov cx,immediate
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_lo: xor cx,cx
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pop ax ;get return address
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pop dx ;get count
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pop bx ;get pointer
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push bx ;restore pointer
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push dx ;restore count
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push ax ;restore return address
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save: mov ax,[bx]
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top: cmp ax,[bx]
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jcxz around
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cmc
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around: ja save
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inc bx
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inc bx
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dec dx
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jnz top
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ret
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Before I end this chapter, let me say that I get a lot of feedback from
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my readers, and it’s much appreciated. Keep those cards, letters, and
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email messages coming. And if any of you know Jeannie Schweigert, have
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her drop me a line and let me know how she’s doing these days....
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------------------------ --------------------------------- --------------------
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[Previous](15-03.html) [Table of Contents](index.html) [Next](16-01.html)
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------------------------ --------------------------------- --------------------
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* * * * *
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Graphics Programming Black Book © 2001 Michael Abrash
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