13 Mjølner BETA Low Level Primitives

13.1 Introduction

This document describes the semantics of the low-level primitives available in the Mjølner implementation of the BETA language. There are currently some syntactic inconveniences. These may be fixed with a grammar change in a future version.

13.2 Low Level Operations

Low level operations on bits, bytes and words are available as described below. Use of these operations may in general be platform dependent.

13.3 Syntax

The syntax is as follows 
%op
i.e., the % indicates, that op is a special low-level operation.

In the following, E, val, and inx are assumed to be integer evaluations, A is an integer object, and R is a repetition object.

13.4 Addressing Conventions

The addressing conventions of bytes, words, longs and bitfields follow the big-endian (Motorola, SPARC etc.) conventions: 


   |------------------------------------------------------------|  
   |31                         long[0]                         0|  
   |-----------------------------|------------------------------|  
   |15         word[0]          0|15          word[1]          0|  
   |--------------|--------------|--------------|---------------|  
   |7   byte[0]  0|7   byte[1]  0|7   byte[2]  0|7   byte[3]   0|  
   |--------------|--------------|--------------|---------------|  
    0                                                         31   
    BitOffset Big-endian -->
                                     BitOffset Little-endian <--

   |              |              |              |        
   BaseAddr       BaseAddr+1     BaseAddr+2     BaseAddr+3

Notice that a BitOffset is addressed from the most significant bit on big-endian architectures, and from the the least significant bit on little-endian architectures (nti, linux).

13.5 Operations

The following operations are available.

13.5.1 Bitwise logical complement (one's complement)

OP:      %Bnot 
usage:   %Bnot E

13.5.2 Bitwise logical and, or, exclusive or

OP:     %Band, %Bor, %Bxor
usage:  E1 OP E2
ex:     E1 %Band E2
Note the B in these operations - B stands for bitwise. A future version may use the syntax %and.

13.5.3 Shift of a long

OP:     %srl       shift right logical
        %sll       shift left logical
        %sra       shift right arithemetic 
        %sla       shift left arithemetic 
        %ror       rotate right
        %rol       rotate left
usage   E1 OP E2
ex:     E1 %sll E2

13.5.4 Get byte/short from a long

OP:     byteNo  -> A.%getByte
        shortNo -> A.%getShort
        longNo  -> A.%getLong
        byteNo  -> A.%getSignedByte 
        shortNo -> A.%getSignedShort
where byteNo is an integer-evaluation in [0,3], shortNo in [0,1] and longNo in [0]. 
Usage:  E1 -> A1.%getByte -> A2
Ex:     1 -> A.%getByte -> B

Note: byteNo -> A.%getLong is the same as A.

13.5.5 Put byte/short into a long

OP:     (val,byteNo)  -> A.%putByte
        (val,shortNo) -> A.%putShort
        (val,longNo)  -> A.%putLong
The same restrictions for byteNo etc. as in Get byte/short from a long apply here. 
usage:  (val,E) -> A.OP
ex.:    (val,3) -> A.%putByte
The same restrictions for byteNo etc. as in Get byte/short from a long apply here.

Note: (val,E)->A.%putLong is the same as val->A.

13.5.6 Get bits from a long

OP:     (pos,width) -> A.%getBits
        (pos,width) -> A.%getSignedBits
where pos, width in [0,31] are integer-evaluations. 
usage: (pos,width) -> A.%getBits -> V

13.5.7 Put bits into a long

OP:     (val,pos,width) -> A.%putBits
where pos, width in [0,31] are integer-evaluations. 
usage:  (V,12,4) -> A.%putBits

13.5.8 This object

Note: This operation is needed in some cases where THIS(P) cannot be used. E.g. inside singular objects in the do-part.
Notice that THIS(Object) will NOT work, you must use the operation below: 
OP:     %thiss object
A reference to the current object is returned. 
Usage:  %thiss object -> S[]
where S is declared as S: ^Object.

BETA Language Modifications - Reference Manual
 © 1999-2002 Mjølner Informatics
[Modified: Sunday October 22nd 2000 at 0:53]