Object Code Accelerator Manual

Preparing Programs for Acceleration

Object Code Accelerator Manual—528144-003

3-6

Arithmetic Left-Shift Sign Bit

In TNS object code (on both TNS and TNS/E processors), arithmetic left-shift

operations preserve the existing sign bit and shift the remaining bits. The operation

discards data shifted out from bit one. An arithmetic left-shift operation loses significant

bits of the arithmetic value if it tries to change the sign bit (bit zero). This loss of

significant bits is a kind of overflow, although the system never traps.

In accelerated object code, an arithmetic left-shift operation does not preserve the sign

bit. Instead, bit zero is included in the bits being shifted. The results might differ from

Figure 3-1. Passing Parameters in Registers

Inherits Registers

Procedure Alpha passes a value in register 7 to procedure Beta. Procedure Beta

assumes that it inherits one register. OCA emits Warning 15 for procedure Beta.

Specify "InheritsR7 Beta" to get a correctly accelerated program.

Returns Registers

Procedure Beta returns a value in register 7 to procedure Alpha. Procedure Alpha

assumes that it inherits one register. OCA emits Warning 15 for procedure Alpha.

Specify "ReturnsR7 Beta" to get a correctly accelerated program.

INT X;

PROC Alpha;

BEGIN

USE A;

A:=4;

CALL Beta;

END;

PROC Beta;

BEGIN

USE B;

X:=B;

END;

VST0301.vdd

INT X;

PROC Alpha;

BEGIN

CALL Beta;

USE A;

X:=A;

END;

PROC Beta;

BEGIN

USE B;

B:=4;

END;