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+
This will add the top two numbers on the
stack and leave the result as a single number.
e.g.
1 2 + . <CR>
will print the value of 1+2 = 3 on the
screen. Note that the two top numbers are removed from the stack, being replaced
by a single number. This is true of most Forth commands, in that they remove the
values which they require to use from the stack and push the result onto the
stack.
The stack in these examples:
N1 = top number on the stack (first to be removed)
N2 = second number on the stack (second to be removed)
N3 = third number on the stack (third to be removed)
To demostrate this, let us push three
numbers onto the stack by typing
HEX 10FA 0019 1F47 <CR>
The
stack will look like this:
|
1F47
|
TOS |
(Top Of Stack) |
|
|
0019
|
|
|
|
|
01fa
|
|
|
|
Note that this illustrate the property
of the stack that is Last In First Out or LIFO, therefore we have:
N1 = 1F47
N2 = 0019
N3 = 01FA
So if we type:
CR . CR . CR . CR <CR>
we get:
1F47
0019
01FA
We will now resume our explanation of
the mathematical operators
-
This will subtract the top number on the
stack from the second number on the stack and leave the result as the top
number. i.e.
N1 = N2 – N1.
e.g.
DECIMAL 7 11 - . <CR>
will print –4 since the stack would
contain
|
N1 |
11
|
TOS |
(Top Of Stack) |
|
N2 |
7
|
|
|
before the subtraction, and
after the subtraction.
*
This will multiply the top two numbers
on the stack and leave the result on the top of the stack. i.e. N1 = N1 * N2.
e.g.
DECIMAL 140 20 * . <CR>
will print 2800.
/
This will divide the second number on
the stack with the first on the stack
e.g.
DECIMAL 1000 500 / . <CR>
will print 2.
MAX
This will leave the greater of the top
two numbers on the stack.
e.g.
371 309 MAX . <CR>
will print 371.
MIN
This will leave the smaller of the top
two numbers on the stack.
e.g.
371 309 MAX . <CR>
will print 309.
ABS
This will leave the absolute value of
the top number on the stack as an unsigned number. i.e. N1 = abs(N1)
e.g.
47 ABS . <CR>
will print 47
-47 ABS . <CR>
will print 47.
MINUS
or NEGATE
This will negate the top number on the
stack. i.e. N1 =
-N1
e.g.
418 MINUS . <CR>
will print -418
-418 MINUS . <CR>
will print 418.
1+
Add 1 to the top number on the stack.
i.e. N1 = N1 + 1
2+
Add 2 to the top number on the stack.
i.e. N1 = N1 + 2
1-
Subtract 1 from the top number on the
stack. i.e. N1 = N1 - 1
2-
Subtract 2 from the top number on the
stack. i.e. N1 = N1 – 2
MOD
This will leave the remainder of N2 / N1
on the top of the stack with the same sign as N2.
e.g.
17 3 MOD . <CR>
will print 2 (17 / 3 = 5 remainder 2).
/MOD
This will leave the remainder and the
quotient on the stack of N2/N1 such that the quotient becomes the top number on
the stack an the remainder becomes the second.
e.g.
17 3 /MOD . CR . <CR>
will print
|
|
5
|
(quotient) |
|
|
2
|
(remainder) |
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