Chapter 3.8, Problem 3.37PP

Explanation of Solution

Array indexing:

• The declaration “T A[N]” where “T” denotes as a data type, “N” an integer constant and “A” denotes an array.
• The starting location of array denotes “x_A”.
• It allocates “L.N” memory bytes that denote a contiguous region.
• The “L” denotes size of data type.
• The array element “i” will be stored at address “x_A+L.i”.

Load Effective Address:

• The load effective address instruction “leaq” is a variant of “movq” instruction.
• The instruction form reads memory to a register, but memory is not been referenced at all.
• The first operand of instruction is a memory reference; the effective address is been copied to destination.
• The pointers could be generated for later references of memory.
• The common arithmetic operations could be described compactly using this instruction.
• The operand in destination should be a register.

Data movement instructions:

• The different instructions are been grouped as “instruction classes”.
• The instructions in a class performs same operation but with different sizes of operand.
• The “Mov” class denotes data movement instructions that copy data from a source location to a destination.
• The class has 4 instructions that includes:
  • movb:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 1 byte data size.
  • movw: 
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 2 bytes data size.
  • movl:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 4 bytes data size.
  • movq:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 8 bytes data size.

Table for array details:

• The array “S” denotes a “short” type and it takes 2 bytes.
• The expression “$\text{S+1}$” denotes a “short*” type, its value is “${\text{x}}_{\text{s}}\text{+2}$”.
• The expression “S[3]” denotes a single value of “short” type, it has 3 values and total size will be 6. The value is “$\text{M}\left[{\text{x}}_{\text{S}}\text{+ 6}\right]$”.
• The expression “&S[i]” denotes “short*” type, the value is “${\text{x}}_{\text{S}}\text{+ 2i}$”.
• The expression “$\text{S}\left[\text{4*i+1}\right]$” denotes a single value of “short” type, it has 4 values and total size will be 8