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Forth Programmer’s Handbook |
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XOR |
( x1 x2 — x3 ) |
Core |
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Return x3, the bit-by-bit exclusive or of x1 with x2. The phrase -1 XOR is equiv- |
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alent to INVERT (one’s complement of the input value). |
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Double-Precision Logical Operations |
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DABS |
( d — +d ) |
Double |
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Return the absolute value of a double-precision stack value. |
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DMAX |
( d1 d2 — d3 ) |
Double |
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Return d3, the larger of d1 and d2. |
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DMIN |
( d1 d2 — d3 ) |
Double |
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Return d3, the lesser of d1 and d2. |
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DNEGATE |
( d — -d ) |
Double |
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Change the sign of a double-precision stack value. Analogous to NEGATE. |
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2.2.3 |
Comparison and Testing Operations |
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These operations leave on the stack a number that is based upon a test of the contents of one or more items on top of the stack. In general, the test is destructive, in that it replaces the item(s) tested with the numerical results of the test. All numbers in Forth may be interpreted as true or false values; zero equals false, and any non-zero value equals true. The words below, which perform explicit tests, return -1 for true. Comparison and testing operations generally precede an IF, WHILE, or UNTIL construct.
You may also use - (minus) or D- as a not-equal test, because they return a non-
!zero difference if the two singleor double-precision numbers are unequal.
Glossary |
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0< |
( n — flag ) |
Core |
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Return flag, which is true if and only if n is less than zero. “zero-less-than” |
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Forth Fundamentals 45
Forth Programmer’s Handbook
0<> |
( n — flag ) |
Core Ext |
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Return flag, which is true if and only if n is not equal to zero. “zero-not-equal” |
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0= |
( n — flag ) |
Core |
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Return flag, which is true if and only if n is equal to zero. “zero-equal” |
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0> |
( n — flag ) |
Core Ext |
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Return flag, which is true if and only if n is greater than zero. “zero-greater-than” |
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< |
( n1 n2 — flag ) |
Core |
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Return flag, which is true if and only if n1 is less than n2. “less-than” |
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<> |
( n1 n2 — flag ) |
Core Ext |
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Return flag, which is true if and only if n1 is not equal to n2. “not-equal” |
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= |
( n1 n2 — flag ) |
Core |
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Return flag, which is true if and only if n1 is equal to n2. “equal” |
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> |
( n1 n2 — flag ) |
Core |
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Return flag, which is true if and only if n1 is greater than n2. “greater-than” |
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D0< |
( d — flag ) |
Double |
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Return flag, which is true if and only if the double-precision value d is less than |
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zero. “D-zero-less” |
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D0= |
( d — flag ) |
Double |
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Return flag, which is true if and only if the double-precision value d is equal to |
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zero. “D-zero-equal” |
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D< |
( d1 d2 — flag ) |
Double |
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Return flag, which is true if and only if d1 is less than d2. “D-less-than” |
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D= |
( d1 d2 — flag ) |
Double |
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Return flag, which is true if and only if d1 is equal to d2. “D-equals” |
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DU< |
( ud1 ud2 — flag ) |
Double Ext |
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Return flag, which is true if and only if ud1 is less than ud2. “D-U-less” |
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FALSE |
( — flag ) |
Core Ext |
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Return a flag that is false (binary zero). |
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46 Forth Fundamentals