[Oberon] Size of LONGINT in ETHOberon

[Jörg]

Dieter

Let's look at the internal representation of a LONGINT (bits 0..31 = 32 bits)
You basically have two parts:
- the highest bit (bit 31) is used for the sign
- the rest (bits 0..30) are the value of the LONGINT.

When using a hexadecimal representation, it's like this
00000000H .. 7FFFFFFFH are positive as the bit 31 is 0
80000000H .. FFFFFFFFH are negative as the bit 31 is 1

Your program calculates 2^x, x from 0..31.
2^31 is in hex 80000000H. So you see, according to the explanation above this is a negative nbr.
The largest positive number is 2^31-1 = 7FFFFFFFH = 2'147'483'647

br
Jörg


Am 12.02.19, 10:36 schrieb "Oberon im Auftrag von Dieter" <oberon-bounces at lists.inf.ethz.ch im Auftrag von d.gloetzel at web.de>:

    I am using:
    
    ETH PlugIn Oberon for WindowsTM / Win32 2.5 (18.12.2010)
          on Windows Vista Version 6.2.9200
    
    According to NW (Programming in Oberon,Steps beyond Pascal and Modula) 
    the size of LONGINT is +/- 2147483647
    
    However, when I run
    
    ==================================================
    
    MODULE powerof2;
    IMPORT Out;
    PROCEDURE power*;
    VAR i : INTEGER; value : LONGINT;
    BEGIN
    i := 0; value := 1;
    WHILE i < 32 DO
    Out.Ln(); Out.Int(i,5); Out.Int(value,20);
    INC(i); value := 2 * value;
    END;
    END power;
    BEGIN
    END powerof2.power
    
    ===================================================
    
    I get
    
    ===================================================
    
      0                   1
         1                   2
         2                   4
         3                   8
         4                  16
         5                  32
         6                  64
         7                 128
         8                 256
         9                 512
        10                1024
        11                2048
        12                4096
        13                8192
        14               16384
        15               32768
        16               65536
        17              131072
        18              262144
        19              524288
        20             1048576
        21             2097152
        22             4194304
        23             8388608
        24            16777216
        25            33554432
        26            67108864
        27           134217728
        28           268435456
        29           536870912
        30          1073741824
        31 -2147483648
    
    =============================
    
    Has anybody got an explanation?
    
    Thanks and bye Dieter
    
    --
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