Demo for query storing
Change-Id: I947bcac841992c3f6cfd01ab337c265b0d01cb70
diff --git a/node_modules/nth-check/compile.js b/node_modules/nth-check/compile.js
new file mode 100644
index 0000000..77f2436
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+++ b/node_modules/nth-check/compile.js
@@ -0,0 +1,40 @@
+module.exports = compile;
+
+var BaseFuncs = require("boolbase"),
+ trueFunc = BaseFuncs.trueFunc,
+ falseFunc = BaseFuncs.falseFunc;
+
+/*
+ returns a function that checks if an elements index matches the given rule
+ highly optimized to return the fastest solution
+*/
+function compile(parsed){
+ var a = parsed[0],
+ b = parsed[1] - 1;
+
+ //when b <= 0, a*n won't be possible for any matches when a < 0
+ //besides, the specification says that no element is matched when a and b are 0
+ if(b < 0 && a <= 0) return falseFunc;
+
+ //when a is in the range -1..1, it matches any element (so only b is checked)
+ if(a ===-1) return function(pos){ return pos <= b; };
+ if(a === 0) return function(pos){ return pos === b; };
+ //when b <= 0 and a === 1, they match any element
+ if(a === 1) return b < 0 ? trueFunc : function(pos){ return pos >= b; };
+
+ //when a > 0, modulo can be used to check if there is a match
+ var bMod = b % a;
+ if(bMod < 0) bMod += a;
+
+ if(a > 1){
+ return function(pos){
+ return pos >= b && pos % a === bMod;
+ };
+ }
+
+ a *= -1; //make `a` positive
+
+ return function(pos){
+ return pos <= b && pos % a === bMod;
+ };
+}
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