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Lecture 2

Decimal ia32 c 39 30 00 00 0 3 9 x8664 c sun

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Unformatted text preview: Washington Byte Ordering     How should bytes within mulJ ­byte word be ordered in memory? Say you want to store 0xaabbccdd   What order will the bytes be stored? Memory 23 University of Washington Byte Ordering     How should bytes within mulJ ­byte word be ordered in memory? Say you want to store 0xaabbccdd   What order will the bytes be stored?   Endianness: big endian vs. lille endian   Two diﬀerent convenGons, used by diﬀerent architectures   Origin: Gulliver’s Travels (see CS:APP2 textbook, secGon 2.1) Memory 24 University of Washington Byte Ordering Example   Big ­Endian (PowerPC, Sun, Internet)   Least signiﬁcant byte has highest address   Lille ­Endian (x86)   Least signiﬁcant byte has lowest address   Example   Variable has 4 ­byte representaGon 0x01234567   Address of variable is 0x100 0x100 Big Endian 0x102 0x103 01 23 45 67 0x100 Lille Endian 0x101 0x101 0x102 0x103 67 45 23 01 Memory 25 University of Washington RepresenJng Integers       int A = 12345; int B = -12345; long int C = 12345; IA32, x86 ­64 A Sun A 39 30 00 00 00 00 30 39 IA32, x86 ­64 B FF FF CF C7 Binary: 0011 0000 0011 1001 3 Hex: Sun B C7 CF FF FF 12345! Decimal:! IA32 C 39 30 00 00 0 3 9 X86 ­64 C Sun C 39 30 00 00 00 00 00 00 00 00 30 39 Two’s complement representaJon for negaJve integers (covered later) Memory 26 University of Washington Memory, Data, and Addressing           Preliminaries RepresenJng informaJon as bits and bytes Organizing and addressing data in memory ManipulaJng data in memory using C Boolean algebra and bit ­level manipulaJons Memory 27 University of Washington Addresses and Pointers in C   & = ‘address of value’ * = ‘value at address’...
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