GEORGE (programming language): Difference between revisions

Revision as of 09:34, 14 June 2012

Revision as of 10:15, 14 June 2012

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and similarly for the other arithmetic operations of subtraction, multiplication, and division.

The algebraic expression a.x**<math>ax^2 + b.xbx + c</math> was written a x dup *× *× b x *× + c + ,

where 'dup' meant 'duplicate the value'.

Following the reverse Polish form, an assignment statement to evaluate the formula <math>y = a.x**ax^2 + b.xbx + c</math> was written as a x dup *× *× b x *× + c + (y) .

The computer evaluated the expression as follows: the values of a, then b, were pushed onto the top of the accumulator stack; 'dup' caused a copy of the top-most value (x) to be pushed onto the top of the accumulator stack; Multiply (*×) caused the top two values, namely, x and x, to be removed (popped) and multiplied, returning the product to the top of the accumulator stack. The second multiply (*×) then caused the top two values on the stack (namely, a and x**2) to be popped and multiplied, and the product (a*xa×x**2) to be pushed onto the top of the accumulator stack. And so on the the remaining components of the expression. The final operation, namely (y), returned the value of the expression to storage without changing the status of the accumulator stack.

Assuming that the value on the top of the accumulator stack was not required immediately, it would be removed (cleared) by using the operator (;).

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The third line fetches a(j), duplicates it, multiplies those two values giving the square, and then stores it in a(j). Note the semicolon (;), which clears (or cancels) the top entry in the accumulator stack. Were this not done, the accumulator would gradually fill up with the squares of the values.

The final line is a vector punch (i.e., print) to write out the ten squares.

{| class="wikitable" style="text-align: center; width: 200px; height: 200px;"

|+ GEORGE coding table<ref><i>Programming Course,</i> School of Electrical Engineering, The University of New South Wales, n.d., p. 24</ref>

|+ GEORGE coding table

|-

! scope="col" |

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|-

! scope="row" | 7

| × || ↑ || 7 || 23 || h || x || (h) || (wx) || ||

|-

! scope="row" | 8

Line 109 ⟶ 108:

| > || || 15 || 31 || p || ω || (p) || (ω) || ||

|}

The above GEORGE coding table assisted in transcribing a program onto punch cards.

Conditional operations were written as jumps, as follows:

if a > 0 go to 5 (which transfers to label 5 if a is greater than zero)

would be written

<pre>0 a > 5 ↑ </pre>

Label 5 was indicated by including *5 elsewhere in the program.

Unconditional transfers were written 5↑

Subroutine calls were made with the down arrow, .g., to call subroutine labelled 17, write 17↓, where the label 17 was encoded using column 3 of the above table.

==Historical note==

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In the second version introduced by 1958, values were held in floating-point form, with

one value per word: 22 bits for the mantissa and 10 bits for the exponent.

Some form of coding table was needed because the printing equipment of the time provided only 26 letters of the alphabet, a decimal point, plus sign, minus sign, decimal point, and slash.

==References==

<references/>