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copied!<h2>C99</h2> <p><strong>Number of characters: 239</strong> (But see below for <strong>209</strong>)</p> <p>compressed function:</p> <pre><code>#define S while(*e==32)++e #define F float F strtof();char*e;F v();F g(){S;return*e++-40?strtof(e-1,&e):v();}F v(){F b,a=g();for(;;){S;F o=*e++;if(!o|o==41)return a;b=g();a=o==43?a+b:o==45?a-b:o==42?a*b:a/b;}}F f(char*x){e=x;return v();} </code></pre> <p>decompressed function:</p> <pre><code>float strtof(); char* e; float v(); float g() { while (*e == ' ') ++e; return *e++ != '(' ? strtof(e-1, &e) : v(); } float v() { float b, a = g(); for (;;) { while (*e == ' ') ++e; float op = *e++; if (op == 0 || op == ')') return a; b = g(); a = op == '+' ? a + b : op == '-' ? a - b : op == '*' ? a * b : a / b; } } float eval(char* x) { e = x; return v(); } </code></pre> <p>Function is not re-entrant.</p> <p><strong>EDIT from Chris Lutz</strong>: I hate to trample on another man's code, but here is a <strong>209</strong>-character version:</p> <pre><code>#define S for(;*e==32;e++) #define X (*e++-40?strtof(e-1,&e):v()) float strtof();char*e;float v(){float o,a=X;for(;;){S;o=*e++;if(!o|o==41)return a;S;a=o-43?o-45?o-42?a/X:a*X:a-X:a+X;}} #define f(x) (e=x,v()) </code></pre> <p>Readable (well, not really very readable, but decompressed):</p> <pre><code>float strtof(); char *e; float v() { float o, a = *e++ != '(' ? strtof(e - 1, &e) : v(); for(;;) { for(; *e == ' '; e++); o = *e++; if(o == 0 || o==')') return a; for(; *e == ' '; e++); // I have no idea how to properly indent nested conditionals // and this is far too long to fit on one line. a = o != '+' ? o != '-' ? o != '*' ? a / (*e++ != '(' ? strtof(e - 1, &e) : v()) : a * (*e++ != '(' ? strtof(e - 1, &e) : v()) : a - (*e++ != '(' ? strtof(e - 1, &e) : v()) : a + (*e++ != '(' ? strtof(e - 1, &e) : v()); } } #define f(x) (e = x, v()) </code></pre> <p>Yeah, <code>f()</code> is a macro, not a function, but it works. The readable version has some of the logic rewritten but not reordered (like <code>o != '+'</code> instead of <code>o - '+'</code>), but is otherwise just an indented (and preprocessed) version of the other one. I keep trying to simplify the <code>if(!o|o==41)return a;</code> part into the <code>for()</code> loop, but it never makes it shorter. I still believe it can be done, but I'm done golfing. If I work on this question anymore, it will be in <a href="http://en.wikipedia.org/wiki/Brainfuck" rel="nofollow noreferrer">the language that must not be named</a>.</p>

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