diff options
Diffstat (limited to 'chapter15/README.md')
| -rw-r--r-- | chapter15/README.md | 49 |
1 files changed, 27 insertions, 22 deletions
diff --git a/chapter15/README.md b/chapter15/README.md index 8ab3378b..1485b04c 100644 --- a/chapter15/README.md +++ b/chapter15/README.md @@ -1,5 +1,8 @@ # Chapter 15: Arrays +[Previous: Chapter 14](../chapter14/README.md) | +[Next: Chapter 16](../chapter16/README.md) + # Table of Contents 1. [Parser changes](#parser) @@ -12,8 +15,8 @@ At long last we introduce arrays! These require more complex addressing math, -which in turn means we need to change how Loads and Stores do addressing - -with true field *offsets* instead of field *names*. This means we also +which in turn means we need to change how Loads and Stores do addressing - +with true field *offsets* instead of field *names*. This means we also will do a struct field *layout* in this chapter. Arrays are created with the standard `new int[len]` syntax, and can be any base @@ -31,7 +34,8 @@ will panic the Evaluator. - `new int[-1]; // Negative length` - `new int[1<<63]; // Too large` - `new int[3.14]; // Not an integer` - + + You can also read [this chapter](https://github.com/SeaOfNodes/Simple/tree/linear-chapter15) in a linear Git revision history on the [linear](https://github.com/SeaOfNodes/Simple/tree/linear) branch and [compare](https://github.com/SeaOfNodes/Simple/compare/linear-chapter14...linear-chapter15) it to the previous chapter. @@ -47,7 +51,7 @@ Arrays are always created with zero/null bodies, so implicitly always allow We make a new array with much the same syntax as making a new object: `new int[99]`. The length is required and is any integer expression, so -e.g. `int[arg]` is an integer array of length `arg`. Multi-dimensional arrays +e.g. `new int[arg]` is an integer array of length `arg`. Multi-dimensional arrays only make the outer dimension; the elements themselves are all null and typed as the next lower dimension array. @@ -57,10 +61,11 @@ post-fix `#` operator; e.g. `ary#`. Example to sum an array: ```java int[] ary = new int[arg]; +int sum = 0; int i = 0; -while( i < ary# ) { - sum = sum + ary[i]; - i = i + 1; +while( i < ary# ) { + sum = sum + ary[i]; + i = i + 1; } ``` @@ -127,14 +132,14 @@ a read before allocation and a later write to an existing object. ## New Address Math -Since arrays need adressing math to index into them, Loads and Stores need a +Since arrays need addressing math to index into them, Loads and Stores need a way to compute an offset. Previously Loads and Stores only worked on structs, -and included the field name within them - thus the impicit addressing was field +and included the field name within them - thus the implicit addressing was field name (e.g. a string lookup!). New in this chapter we create a struct *layout* and compute field offsets to all structs. Loads and Stores now take an `off` instead of a field name, and the field -name is included for debugging only. +name is included for debugging only. ```java public MemOpNode(String name, int alias, Type glb, Node mem, Node ptr, Node off) { @@ -178,8 +183,8 @@ mod 8. This means the actual field offset and the field declaration order are ```java struct s { - int8 b; // log_size=0 - uint16 char; // log_size=1 + i8 b; // log_size=0 + u16 char; // log_size=1 Person p; // log_size=2 flt pi; // log_size=3 } @@ -187,9 +192,9 @@ struct s { struct s { flt pi; // offset= 0, log_size=3 Person p; // offset= 8, log_size=2 - uint16 char; // offset=12, log_size=1 - int8 b; // offset=13, log_size=0 - void pad; // offset=14, size = 2 + u16 char; // offset=12, log_size=1 + i8 b; // offset=14, log_size=0 + void pad; // offset=15, size = 1 } // size =16 ``` @@ -200,7 +205,7 @@ this could be changed at a later date to support a larger range of pointers. integer ranges. Other ranges are possible in Simple via `compute` calls, but these will never show up as base field types: - `struct S { int16 x; }` + `struct S { i16 x; }` Here `x` will have offset 0 and size 2 bytes, and `S` will be padded to size 8. @@ -221,17 +226,17 @@ This means the IR for: `x[i]` becomes `16/*base*/ + (i << 3/*scale*/)` becomes `Load(mem,x,Add(Shl(i,3),16))` - - + + `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 -Included in the test cases in a simple rolling sum, and a Sieve of Eratosthenes. +Included in the test cases is a simple rolling sum, and a Sieve of Eratosthenes. ```java int i=0; @@ -241,7 +246,7 @@ while( i < ary# ) { } ``` -Here we really see the lack of a `i++` operator and a `for` loop. You can +Here we really see the lack of an `i++` operator and a `for` loop. You can imagine another syntax: ```java @@ -249,6 +254,6 @@ for( int i=0; i < ary#; i++ ) ary[i] = i; ``` -that would be entirely syntatic-sugar over the existing parser, but would +that would be entirely syntactic-sugar over the existing parser, but would really help make array looping syntax clearer. There are lots of options here, which should really be the focus of another chapter! |