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| author | Quentin Carbonneaux <quentin.carbonneaux@yale.edu> | 2016-03-11 13:13:32 -0500 |
|---|---|---|
| committer | Quentin Carbonneaux <quentin.carbonneaux@yale.edu> | 2016-03-11 13:22:44 -0500 |
| commit | 01278dbeca4db1a42c709e65bc44110f5db4ad63 (patch) | |
| tree | 9522c7b7d20a2cc3659b2a27f2cfee7390eeb8e8 | |
| parent | 5f80243857bf5282f6edbc050eb4a87937a75ed0 (diff) | |
| download | roux-01278dbeca4db1a42c709e65bc44110f5db4ad63.tar.gz | |
document constants
| -rw-r--r-- | doc/il.txt | 47 |
1 files changed, 44 insertions, 3 deletions
diff --git a/doc/il.txt b/doc/il.txt index e802bb8..c656d79 100644 --- a/doc/il.txt +++ b/doc/il.txt @@ -14,9 +14,7 @@ 2. <@ Types > * <@ Simple Types > * <@ Subtyping > - 3. Immediate Constants - * Semantics - * Floating Sugar + 3. <@ Immediate Constants > 4. <@ Definitions > * <@ Aggregate Types > * <@ Data > @@ -149,6 +147,49 @@ The rationale is that the 32 high bits of the extended long value could very well be zeroes or the result of a sign extension of the word. +- 3. Immediate Constants +------------------------ + + `bnf + CONST := + ['-'] NUMBER # Decimal integer + | 's_' FP # Single-precision float + | 'd_' FP # Double-precision float + | $IDENT # Global symbol + +Throughout the IL, constants are specified with a unified +syntax and semantics. Constants are immediates, meaning +that they can be used directly in instructions; there is +no need for a "load constant" instruction. + +The representation of integers is two's complement. +Floating point numbers are represented using the +single-precision and double-precision formats of the +EEE 754 standard. + +Consants specify a sequence of bits and are untyped. +They are always parsed as 64 bits blobs. Depending on +the context surrounding one constant, only some of its +bits are used. For example, in the program below, the +two variables defined have the same value since they +are defined in a word (32 bits) context. + + %x =w sub -1, 0 + %y =w sub 4294967295, 0 + +Because specifying floating point constants by their bits +makes the code less readable, syntactic sugar is provided +to express them. Standard scientific notation is used with +a prefix of `s_` for single and `d_` for double-precision +numbers. Once again, the following example defines twice +the same double-precision constant. + + %x =d add d_0, d_-1 + %y =d add d_0, -4616189618054758400 + +Global symbols can also be used directly as constants, +they will be resolved and turned to actual numeric +constants by the linker. - 4. Definitions ---------------- |