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Diffstat (limited to 'chapter15/README.md')
| -rw-r--r-- | chapter15/README.md | 15 |
1 files changed, 9 insertions, 6 deletions
diff --git a/chapter15/README.md b/chapter15/README.md index 8e122b4c..009decc5 100644 --- a/chapter15/README.md +++ b/chapter15/README.md @@ -25,7 +25,7 @@ will panic the Evaluator. The Parser changes to support arrays are fairly minimal. The main change is when parsing a `type()` we look for array syntax: `int[]` is now a valid type. -Any amount of arrays are allowed, and the base type can be any type so +Any dimension of arrays are allowed, and the base type can be any type so e.g. `Person[][]?` is a two-dimensional array of `Person`s which might be null. Arrays are always created with zero/null bodies, so implicitly always allow @@ -35,7 +35,7 @@ We make a new array with much the same syntax as making a new object: `new int[99][99]`. The length is required and is any integer expression, so e.g. `int[arg]` is an integer array of length `arg`. -Arrays implicit have two fields: the length and the body. The length is a +Arrays implicitly have two fields: the length and the body. The length is a read-only field set when the array is allocated; it is referenced with the post-fix `#` operator; e.g. `ary#`. Example to sum an array: @@ -61,7 +61,7 @@ optimized - but Simple the compiler is not targeting complex vectorization. Arrays have a unique type, which is actually just a `TypeStruct` with fields named `#` and `[]`. Since these are not available as field names from within -the Parser, users can write their own structs which get confused as arrays. +the Parser, users cannot write their own structs which get confused as arrays. These `TypeStruct` arrays otherwise behave exactly as a `TypeStruct`. @@ -130,7 +130,8 @@ mod 8. This means the actual field offset and the field declaration order are Person p; // offset= 8, log_size=2 uint16 char; // offset=12, log_size=1 int8 b; // offset=13, log_size=0 - } // size =16 + void pad; // offset=14, size = 2 + } // size =16 ``` @@ -148,7 +149,7 @@ Here `x` will have offset 0 and size 2 bytes, and `S` will be padded to size 8. `S s = new S; s.x = 3;` The same `x` field now holds either a 0 or a 3, so the `TypeInteger` for `x` -will be a range `[0-3]`... but this is not used to compute the field size. +will be a range `[0-3]` which could be represented in just 2 bits ... but this is not used to compute the field size. ## Some Simple Address Math Peeps @@ -166,7 +167,9 @@ This means the IR for: `x[i+1]` becomes `16/*base*/ + ((i+1) << 3/*scale*)` becomes `Load(mem,x,Add(Shl(i,3),24))` - + +Notice the `idx+1` folds the `+1` into the base math. + ## Discussion |