commit 01278dbeca4db1a42c709e65bc44110f5db4ad63
parent 5f80243857bf5282f6edbc050eb4a87937a75ed0
Author: Quentin Carbonneaux <quentin.carbonneaux@yale.edu>
Date: Fri, 11 Mar 2016 13:13:32 -0500
document constants
Diffstat:
| M | doc/il.txt | | | 47 | ++++++++++++++++++++++++++++++++++++++++++++--- |
1 file changed, 44 insertions(+), 3 deletions(-)
diff --git 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
----------------
