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#ifndef _ARROW
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#define _ARROW
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struct _arrow_mem {struct _arrow_reg {_Bool _first; } _reg; };
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extern struct _arrow_mem *_arrow_alloc ();
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extern void _arrow_dealloc (struct _arrow_mem *);
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#define _arrow_DECLARE(attr, inst)\
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attr struct _arrow_mem inst;
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#define _arrow_LINK(inst) do {\
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;\
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} while (0)
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#define _arrow_ALLOC(attr, inst)\
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_arrow_DECLARE(attr, inst);\
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_arrow_LINK(inst)
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#define _arrow_init(self) {}
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#define _arrow_clear(self) {}
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#define _arrow_step(x,y,output,self) ((self)->_reg._first?((self)->_reg._first=0,(*output = x)):(*output = y))
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#define _arrow_reset(self) {(self)->_reg._first = 1;}
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/* Step macro for specialized arrows of the form: (true -> false) */
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#define _once_step(output,self) { *output = (self)->_reg._first; if ((self)->_reg._first) { (self)->_reg._first=0; }; }
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#endif
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