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[CHANGED] subtraction is now implemented it terms of ADD.

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sjs 2009-05-15 09:37:44 -07:00
parent e7a6162e7b
commit 785f229eec
1 changed files with 6 additions and 7 deletions
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13
compiler.rb
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@ -150,14 +150,13 @@ class Compiler
# Parse and translate a single factor. Result is in eax. # Parse and translate a single factor. Result is in eax.
def factor def factor
case if @look == '('
when @look == '('
match('(') match('(')
expression expression
match(')') match(')')
when alpha?(@look) elsif alpha?(@look)
identifier identifier
when digit?(@look) elsif digit?(@look)
x86_mov(:eax, get_num) x86_mov(:eax, get_num)
else else
expected("a number, identifier, or an expression wrapped in parens") expected("a number, identifier, or an expression wrapped in parens")
@ -250,9 +249,9 @@ class Compiler
# left in eax. The 1st term (a) is expected on the stack. # left in eax. The 1st term (a) is expected on the stack.
def subtract def subtract
match('-') match('-')
term # Result is in eax. term # Result, b, is in eax.
x86_sub(:eax, '[esp]') # Subtract a from b (this is backwards). x86_neg(:eax) # Fake the subtraction. a - b == a + -b
x86_neg(:eax) # Fix things up. -(b-a) == a-b x86_add(:eax, '[esp]') # Add a and -b.
end end
# Parse an addition operator and the 2nd term (b). The result is # Parse an addition operator and the 2nd term (b). The result is