ST20-C1 datasheet(40/205 Pages) STMICROELECTRONICS

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4.4 Arithmetic

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ldl Xhi; ldl Ylo; umac; stl Z1;

ldl Xhi; ldl Yhi; umac; rev; stl Z3;

ldc 0; rev; ldl Z2; addc; stl Z2;

ldl Z3; addc; stl Z3

This gives a quadruple length unsigned result

Z, where Z0 is the least significant and

Z3 the most significant word of Z.

4.4.6

Object length conversion

Object length conversion operations are provided by the instructions listed in Table

4.7.

Section 3.1 explains that data can be represented in data objects of various sizes.

This section describes the instructions that can be used to convert between these

representations.

Most of the ST20-C1 integer arithmetic instructions operate on signed integers held in

the evaluation stack registers as 32-bit objects, and produce results in this form.

Object length conversion is important for conversion of high level language data types.

The ST20-C1 therefore provides instructions that allow a byte or half-word signed

integer to be sign extended to 32-bits by copying the sign bit to all the bits that were

previously not significant, as sho wn in Figure 3.2. The sign extension is performed on

the value in the Areg and the result is placed in the Areg. The other registers are not

affected.

xbword extends a signed byte to a word by copying bit 7 into bits 8 to 31. xsword

extends a signed half-word to a word by copying bit 15 into bits 16 to 31.

lsxinc loads a sixteen bit value, sign extends it to 32 bits and increments the address

by two bytes. This is the same as:

lsinc; xsword;

Mnemonic

Name

xbword

sign extend byte to word

xsword

sign extend sixteen to word

Table 4.7 Object length conversion instructions

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