Lecture #26

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Language Translation

Now Rules R4 and R5

Syntax Rule Semantic Rules

 R4: <e>i->(<e>j+<e>k)

`M(<e>i) = createname`
	`code(<e>i)=`	`code(<e>j)`
	`code(<e>k)`
	`COPY AX,M(<e>j)`
	`ADD AX,M(<e>k)`
	`COPY M(<e>i),AX`

Says code for <e>i is code to calculate expression <e>j followed by code to calculate expression <e>k and code to add them together and store that sum into Memory associated with <e>i

Syntax Rule Semantic Rules

 R5: <e>i->(<e>j*<e>k)

`M(<e>i) = createname`
	`code(<e>i)=`	`code(<e>j)`
	`code(<e>k)`
	`COPY AX,M(<e>j)`
	`MUL AX,M(<e>k)`
	`COPY M(<e>i),AX`

Says code for <e>i is code to calculate expression <e>j followed by code to calculate expression <e>k and code to multiply them together and store that sum into Memory associated with <e>i

Basically rules R4 and R5 are identical except that the + and ADD in one are replace by the * and MUL in the other.

Look at Example from Pages 275-276 of book
It does Z = (X + Y)

More complicated example for U1 = (X + (Y * Z)) also in book. Look at it.

Rules for Looping
Sequence of statements

Syntax Rule Semantic Rules

`R6: <q>i ->`	`<s>j`
	`<q>k`

`code(<q>i) =`	`code(<s>j)`
	`code(<q>k)`

Syntax Rule	Semantic Rules
`R7: <q>i -> <s>j`	`code(<q>i) = code(<s>j)`

Says code for a sequence of statements is the code for the first statement followed by the code for the next statement, etc.

Compound Statement

Syntax Rule Semantic Rules

`R8: <c>i ->`	`{`
	`<q>j`
	`}`

 code(<c>i) = code(<q>j)

While Statement

Syntax Rule Semantic Rules

`R9: <s>i->`	`while (<n>j < <e>k)`
	`<c>h`

`M(<s>i) = createname`
`M'(<s>i) = createname`
`code(<s>i) =`
`M(<s>i)`	`code(<e>k)`
	`COPY AX,M(<n>j)`
	`CMP AX,M(<e>k)`
	`JNB M'(s<n>)`
	`code(<c>h)`
	`JMP M(<s>i)`
`M'(<s>i)`	`NO-OP`

Cleanup Translation
Some code generated that can be removed.
Important: Everything done by simple substitution
Everything "adds up"

code( { <s>1;<s>2;<s>3 } )
is
code(<s>1)
code(<s>2)
code(<s>3)