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subtraction

summary

    This subchapter looks at subtraction.

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stub section

    This subchapter is a stub section. It will be filled in with instructional material later. For now it serves the purpose of a place holder for the order of instruction.

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subtraction

    This subchapter looks at subtraction.

number systems

    Here is a little bit of college level work on subtraction.

    A system of numbers os considered to be closed under an operation if it reproduces itself.

    S is a set of numbers. S is closed with respect to subtraction if for any two numbers a and b in the set S, the difference a - b is also a number in the set S. A set closed with respect to subtraction is called a modul.

    The set of all integers {0, ±1, ±2, ±3, …} is a modul. The set of natural numbers {1, 2, 3, …} is not a modul.

    The set of all even integers {0, ±2, ±4, ±6, …} is a modul.

    The set of all rational numbers is a modul.

    The set of all real numbers is a modul.

    The set of all complex numbers is a modul.

    The set of all purely imagiunary numbers ib is a modul.

    A theorem regarding moduls:

    (a) A modul always contains the number zero (0).

    (b) If a modul contains the number a then it also contains the number -a.

    (c) A modul is always closed with respect to addition.

    Another theorem regarding moduls:

    Any modul M containing only integers includes all multiples of the greatest common divisor of the numbers in M.

assembly language instructions

    For most processors, integer arithmetic is faster than floating point arithmetic. This can be reversed in special cases such digital signal processors.

    On many processors, floating point arithmetic is in an optional unit or optional coprocessor rather than being included on the main processor. This allows the manufacturer to charge less for the business machines that don’t need floating point arithmetic.

    The basic four integer arithmetic operations are addition, subtraction, multiplication, and division. Arithmetic operations can be signed or unsigned (unsigned is useful for effective address computations). Some older processors don’t include hardware multiplication and division. Some processors don’t include actual multiplication or division hardware, instead looking up the answer in a massive table of results embedded in the processor.

    A specialized, but common, form of subtraction is an decrement instruction, which subtracts one from the contents of a register or memory location. For address computations, “decrement” may mean the subtraction of a constant other than one. Some processors have “short” or “quick” subtraction instructions that extend decrement to include a small range of values.

• SUB Subtract; DEC VAX; signed subtraction of scalar quantities (8, 16, or 32 bit integer or 32, 64, or 128 bit floating point) in general purpose registers or memory, available in two operand (first operand subtracted from second operand with result replacing second operand) and three operand (first operand subtracted from second operand with result placed in third operand) (SUBB2 integer subtract byte 2 operand, SUBB3 integer subtract byte 3 operand, SUBW2 integer subtract word 2 operand, SUBW3 integer subtract word 3 operand, SUBL2 integer subtract long 2 operand, SUBL3 integer subtract long 3 operand) (SUBF2 subtract float 2 operand, SUBF3 subtract float 3 operand, SUBD2 subtract double float 2 operand, SUBD3 subtract double float 3 operand, SUBG2 subtract G float 2 operand, SUBG3 subtract G float 3 operand, SUBH2 subtract H float 2 operand, SUBH3 subtract H float 3 operand); clears or sets flags
• SUB Subtract Integers; Intel 80x86; integer subtraction of the contents of a register or memory (8, 16, or 32 bits) from a memory location or a register; sets or clear flags
• SUB Subtract; Motorola 680x0, Motorola 68300; signed subtract of the contents of a data register (8, 16, or 32 bits) from a memory location or subtracts the contents of a memory location (8, 16, or 32 bits) from a data register; sets or clear flags
• SUB Subtract; MIX; subtract word or partial word field contents of memory from A-register (accumulator), overflow toggle possibly set
• SR Subtract Register; IBM 360/370; RR format; signed subtract of the contents of a general purpose register (32 bits) from a general purpose register (32 bits); register to register only; sets or clears flags
• S Subtract; IBM 360/370; RX format; signed subtract of the contents of a memory location (32 bits) from a general purpose register (32 bits); main memory to register only; sets or clears flags
• SH Subtract Half-word; IBM 360/370; RX format; signed subtract of the contents of a memory location (16 bits) from a general purpose register (low order 16 bits); main memory to register only; sets or clears flags
• SUBA Subtract Address; Motorola 680x0, Motorola 68300; unsigned subtract of the contents of a memory location or register (16 or 32 bits) from an address register; does not modify flags
• SUBI Subtract Immediate; Motorola 680x0, Motorola 68300; signed subtract of immediate data (8, 16, or 32 bits) from a register or memory location; sets or clears flags
• SUBQ Subtract Quick; Motorola 680x0, Motorola 68300; signed subtract of an immediate value of 1 to 8 inclusive from a register or memory lcoation; sets or clears flags for data registers and memory locations, does not modify flags for an address register
• DEC Decrement; DEC VAX; decrements the integer contents of a general purpose register or contents of memory (DECB byte, DECW word, DECL longword); equivalent to SUBx2 #1, sum, but shorter and executes faster; clears or sets flags
• DEC Decrement by 1; Intel 80x86; decrements the contents of a register or memory (8, 16, or 32 bits); sets or clear flags (does not modify carry flag)
• SBWC Subtract With Carry; DEC VAX; integer subtraction (32 bit) in general purpose registers or memory, first operand and the C (carry) flag subtracted from second operand with result replacing second operand; used for extended precision subtraction; clears or sets flags
• SBB Subtract Integers with Borrow; Intel 80x86; integer subtraction of the contents of a register or memory (8, 16, or 32 bits) and carry flag from a memory location or a register; sets or clear flags
• SUBX Subtract Extended; Motorola 680x0, Motorola 68300; (signed subtract of a data register [8, 16, or 32 bits] and the extend bit from a data register) or (signed subtract of the contents of memory location [8, 16, or 32 bits] and the extend bit from the contents of another memory location while predecrementing both the source and destination address pointer registers), used to implement multi-precision integer arithmetic; sets or clears flags

See also Integer Arithmetic Instructions in Assembly Language and Floating Point Arithmetic Instructions in Assembly Language

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