69 lines
3 KiB
Text
69 lines
3 KiB
Text
# Conversion to/from negative base numbers #
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# Note - no checks for valid bases or digits bases -2 .. -63 are handled #
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# A-Z represent the digits 11 .. 35, a-z represent the digits 36 .. 61 #
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# the digit 62 is represented by a space #
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# 1 2 3 4 5 6 #
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# 01234567890123456789012345678901234567890123456789012 #
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[]CHAR base digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz "[ AT 0 ];
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# returns s decoded to an integer from the negative base b #
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PRIO FROMNBASE = 9;
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OP FROMNBASE = ( STRING s, INT b )LONG INT:
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BEGIN
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LONG INT result := 0;
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LONG INT base multiplier := 1;
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FOR d pos FROM UPB s BY -1 TO LWB s DO
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INT digit = IF s[ d pos ] = " "
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THEN 62
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ELIF s[ d pos ] >= "a"
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THEN ( ABS s[ d pos ] + 36 ) - ABS "a"
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ELIF s[ d pos ] >= "A"
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THEN ( ABS s[ d pos ] + 10 ) - ABS "A"
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ELSE ABS s[ d pos ] - ABS "0"
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FI;
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result +:= base multiplier * digit;
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base multiplier *:= b
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OD;
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result
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END # FROMNBASE # ;
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OP FROMNBASE = ( CHAR c, INT b )LONG INT: STRING(c) FROMNBASE b;
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# returns n encoded as a string in the negative base b #
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PRIO TONBASE = 9;
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OP TONBASE = ( LONG INT n, INT b )STRING:
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BEGIN
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STRING result := "";
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LONG INT v := n;
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WHILE
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INT d := SHORTEN IF v < 0 THEN - ( ABS v MOD b ) ELSE v MOD b FI;
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v OVERAB b;
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IF d < 0
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THEN
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d -:= b;
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v +:= 1
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FI;
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base digits[ d ] +=: result;
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v /= 0
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DO SKIP OD;
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result
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END # TONBASE # ;
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# tests the TONBASE and FROMNBASE operators #
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PROC test n base = ( LONG INT number, INT base, STRING expected )VOID:
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BEGIN
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PROC expect = ( BOOL result )STRING: IF result THEN "" ELSE " INCORRECT" FI;
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STRING encoded = number TONBASE base;
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LONG INT decoded = encoded FROMNBASE base;
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print( ( whole( number, 0 ), " encodes to: ", encoded ) );
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print( ( " base ", whole( base, 0 ), expect( encoded = expected ), newline ) );
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print( ( encoded, " decodes to: ", whole( decoded, 0 ) ) );
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print( ( " base ", whole( base, 0 ), expect( decoded = number ), newline ) )
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END # test n base # ;
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test n base( 10, -2, "11110" );
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test n base( 146, -3, "21102" );
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test n base( 15, -10, "195" );
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# The defining document for ALGOL 68 spells the name "Algol 68" on the cover, though inside it is "ALGOL 68" #
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# at the risk of "judging a language by it's cover", we use "Algol 68" as the name here... #
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test n base( - LONG 36492107981104, -63, "Algol 68" )
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