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| author | Hans Boehm <hboehm@google.com> | 2015-10-10 00:18:42 +0000 |
|---|---|---|
| committer | Android Git Automerger <android-git-automerger@android.com> | 2015-10-10 00:18:42 +0000 |
| commit | ed234b7d8fb8e480cbb83ff8eb83297431cc572a (patch) | |
| tree | f255bbc20569082c0a3ad244622ad0db571bd883 /docs/implementation-overview.html | |
| parent | d6136e699d360e920cd11036056b62a1923e4166 (diff) | |
| parent | c49a1ffaa2801c042bb3f2d3d2ffbb5f4e8f8a21 (diff) | |
| download | android_packages_apps_ExactCalculator-ed234b7d8fb8e480cbb83ff8eb83297431cc572a.tar.gz android_packages_apps_ExactCalculator-ed234b7d8fb8e480cbb83ff8eb83297431cc572a.tar.bz2 android_packages_apps_ExactCalculator-ed234b7d8fb8e480cbb83ff8eb83297431cc572a.zip | |
am c49a1ffa: am a4eb1c07: Merge "Add docs directory and contents" into mnc-dr-dev
* commit 'c49a1ffaa2801c042bb3f2d3d2ffbb5f4e8f8a21':
Add docs directory and contents
Diffstat (limited to 'docs/implementation-overview.html')
| -rw-r--r-- | docs/implementation-overview.html | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/docs/implementation-overview.html b/docs/implementation-overview.html new file mode 100644 index 0000000..a06e73b --- /dev/null +++ b/docs/implementation-overview.html @@ -0,0 +1,51 @@ +<!doctype html> +<html> +<head> +<title>Calculator Implementation Overview</title> +<meta charset="UTF-8"> +</head> +<h1>M Calculator Implementation Overview</h1> +<p>Although the appearance of the calculator has changed little from Lollipop, and some of the UI +code is indeed the same, the rest of the code has changed substantially. Unsurprisingly, +<b>Calculator.java</b> implements the main UI. The other major parts of the implementation +are:</p> + +<p><b>CR.java</b> in <b>external/crcalc</b> provides the underlying demand-driven ("constructive +real") arithmetic implementation. Numbers are represented primarily as objects with a method that +can compute arbitrarily precise approximations. The actual arithmetic performed by these methods +is based on Java's <tt>java.util.BigInteger</tt> arithmetic, with appropriate implicit +scaling.</p> + +<p><b>BoundedRational.java</b> is a rational arithmetic package that is used to provide finite +exact answers in "easy" cases. It is used primarily to determine when an approximation provided +by CR.java is actually exact. This is used in turn both to limit the length of displayed results +and scrolling, as well as to identify errors such as division by zero, that would otherwise result +in timeouts during computations. It is in some sense not needed to produce correct results, but +it significantly improves the usability of the calculator. It is also used for the "display as +fraction" option in the overflow menu.</p> + +<p><b>CalculatorExpr.java</b> implements calculator arithmetic expressions. It supports editing, +saving, restoring, and evaluation of expressions. Evaluation produces a constructive real (CR) +and possibly a BoundedRational result. Unlike the "arity" library used in earlier versions, the +underlying expression is represented as a sequence of "tokens", many of which are represented by +Button ids, not as a character string.</p> + +<p><b>Evaluator.java</b> implements much of the actual calculator logic, particularly background +expression evaluation. Expression evaluation here includes both using CalculatorExpr.java to +evaluate the expression, and then invoking the resulting CR value to actually produce finite +approximations and convert them to decimal. Two types of expression evaluation are supported: +(1) Initial evaluation of the expression and producing an initial decimal approximation, and (2) +reevaluation to higher precision. (1) is invoked directly from the Calculator UI, while (2) is +invoked from the calculator display, commonly in response to scrolling. When the display requests +a result, a "result" is immediately returned, though it may contains blank placeholders. The +display is then notified when the real result becomes available.</p> + +<p><b>CalculatorText.java</b> is the TextView subclass used to display the formula.</p> + +<p><b>CalculatorResult.java</b> is the TextView subclass used to display the result. It handles +result formatting, scrolling, etc. After the user hits "=", the CalculatorResult widget moves +into the top position, replacing the formula display. Currently it remains in that position until +the formula is again modified.</p> +</body> +</html> + |