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Full Discussion: AWK equation evaluation.
Top Forums Shell Programming and Scripting AWK equation evaluation. Post 302146814 by srdgeo on Thursday 22nd of November 2007 09:59:12 AM
Old 11-22-2007
AWK equation evaluation.
Hi,

Is there a way to evaluate an equation contained in a string within an AWK script?

For example:
A = "(5*2)-1" (this equation is read from a file and varies line by line)

In this example, I can't see any way to get an answer of 9 unless I do:

cmd = "awk 'BEGIN{print "A"}'"
cmd | getline A

The above method works fine but it's rather slow when dealing with large files!

Does anybody know of a better way of achieving the same result within the main AWK script?

Any help and advice appreciated.

Steve
 

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LEARN ABOUT CENTOS

glblendequation

GLBLENDEQUATION(3G)						   OpenGL Manual					       GLBLENDEQUATION(3G)

NAME

       glBlendEquation - specify the equation used for both the RGB blend equation and the Alpha blend equation

C SPECIFICATION

       void glBlendEquation(GLenum mode);

       void glBlendEquationi(GLuint buf, GLenum mode);

PARAMETERS

       buf
	   for glBlendEquationi, specifies the index of the draw buffer for which to set the blend equation.

       mode
	   specifies how source and destination colors are combined. It must be GL_FUNC_ADD, GL_FUNC_SUBTRACT, GL_FUNC_REVERSE_SUBTRACT, GL_MIN,
	   GL_MAX.

DESCRIPTION

       The blend equations determine how a new pixel (the ''source'' color) is combined with a pixel already in the framebuffer (the
       ''destination'' color). This function sets both the RGB blend equation and the alpha blend equation to a single equation.  glBlendEquationi
       specifies the blend equation for a single draw buffer whereas glBlendEquation sets the blend equation for all draw buffers.

       These equations use the source and destination blend factors specified by either glBlendFunc() or glBlendFuncSeparate(). See glBlendFunc()
       or glBlendFuncSeparate() for a description of the various blend factors.

       In the equations that follow, source and destination color components are referred to as R s G s B s A s and R d G d B d A d, respectively.
       The result color is referred to as R r G r B r A r. The source and destination blend factors are denoted s R s G s B s A and d R d G d B d
       A, respectively. For these equations all color components are understood to have values in the range 0 1.

       +-----------------------------+---------------------------------------------------+---------------------------------------------------+
       |			     |							 |						     |
       |			Mode |			       RGB			 |			   Alpha		     |
       |			     | Components					 | Component					     |
       |			     |							 |						     |
       +-----------------------------+---------------------------------------------------+---------------------------------------------------+
       |GL_FUNC_ADD		     | <div>						 | <div>					     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				       Rr		 |				   Ar		     |
       |			     |				       =		 |				   =		     |
       |			     |							 |						     |
       |			     |					   R		 |				       A	     |
       |			     |					   s		 |				       s	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   s		 |				       s	     |
       |			     |					   R		 |				       A	     |
       |			     |							 |						     |
       |			     |					   +		 |				       +	     |
       |			     |					   R		 |				       A	     |
       |			     |					   d		 |				       d	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   d		 |				       d	     |
       |			     |					   R		 |				       A	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |			       </div>			 |			   </div>		     |
       |			     |			       <div>			 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				       Gr		 |						     |
       |			     |				       =		 |						     |
       |			     |							 |						     |
       |			     |					   G		 |						     |
       |			     |					   s		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   s		 |						     |
       |			     |					   G		 |						     |
       |			     |							 |						     |
       |			     |					   +		 |						     |
       |			     |					   G		 |						     |
       |			     |					   d		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   d		 |						     |
       |			     |					   G		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |			       </div>			 |						     |
       |			     |			       <div>			 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				       Br		 |						     |
       |			     |				       =		 |						     |
       |			     |							 |						     |
       |			     |					   B		 |						     |
       |			     |					   s		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   s		 |						     |
       |			     |					   B		 |						     |
       |			     |							 |						     |
       |			     |					   +		 |						     |
       |			     |					   B		 |						     |
       |			     |					   d		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   d		 |						     |
       |			     |					   B		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |			       </div>			 |						     |
       +-----------------------------+---------------------------------------------------+---------------------------------------------------+
       |GL_FUNC_SUBTRACT	     | <div>						 | <div>					     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				       Rr		 |				   Ar		     |
       |			     |				       =		 |				   =		     |
       |			     |							 |						     |
       |			     |					   R		 |				       A	     |
       |			     |					   s		 |				       s	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   s		 |				       s	     |
       |			     |					   R		 |				       A	     |
       |			     |							 |						     |
       |			     |					   -		 |				       -	     |
       |			     |					   R		 |				       A	     |
       |			     |					   d		 |				       d	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   d		 |				       d	     |
       |			     |					   R		 |				       A	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |			       </div>			 |			   </div>		     |
       |			     |			       <div>			 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				       Gr		 |						     |
       |			     |				       =		 |						     |
       |			     |							 |						     |
       |			     |					   G		 |						     |
       |			     |					   s		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   s		 |						     |
       |			     |					   G		 |						     |
       |			     |							 |						     |
       |			     |					   -		 |						     |
       |			     |					   G		 |						     |
       |			     |					   d		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   d		 |						     |
       |			     |					   G		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |			       </div>			 |						     |
       |			     |			       <div>			 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				       Br		 |						     |
       |			     |				       =		 |						     |
       |			     |							 |						     |
       |			     |					   B		 |						     |
       |			     |					   s		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   s		 |						     |
       |			     |					   B		 |						     |
       |			     |							 |						     |
       |			     |					   -		 |						     |
       |			     |					   B		 |						     |
       |			     |					   d		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   d		 |						     |
       |			     |					   B		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |			       </div>			 |						     |
       +-----------------------------+---------------------------------------------------+---------------------------------------------------+
       |GL_FUNC_REVERSE_SUBTRACT     | <div>						 | <div>					     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Rr		 |				       Ar	     |
       |			     |					   =		 |				       =	     |
       |			     |							 |						     |
       |			     |					       R	 |					   A	     |
       |			     |					       d	 |					   d	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					       d	 |					   d	     |
       |			     |					       R	 |					   A	     |
       |			     |							 |						     |
       |			     |					       -	 |					   -	     |
       |			     |					       R	 |					   A	     |
       |			     |					       s	 |					   s	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					       s	 |					   s	     |
       |			     |					       R	 |					   A	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |			       </div>		     |
       |			     |				   <div>		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Gr		 |						     |
       |			     |					   =		 |						     |
       |			     |							 |						     |
       |			     |					       G	 |						     |
       |			     |					       d	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					       d	 |						     |
       |			     |					       G	 |						     |
       |			     |							 |						     |
       |			     |					       -	 |						     |
       |			     |					       G	 |						     |
       |			     |					       s	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					       s	 |						     |
       |			     |					       G	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |						     |
       |			     |				   <div>		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Br		 |						     |
       |			     |					   =		 |						     |
       |			     |							 |						     |
       |			     |					       B	 |						     |
       |			     |					       d	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					       d	 |						     |
       |			     |					       B	 |						     |
       |			     |							 |						     |
       |			     |					       -	 |						     |
       |			     |					       B	 |						     |
       |			     |					       s	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					       s	 |						     |
       |			     |					       B	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |						     |
       +-----------------------------+---------------------------------------------------+---------------------------------------------------+
       |GL_MIN			     | <div>						 | <div>					     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Rr		 |				       Ar	     |
       |			     |					   =		 |				       =	     |
       |			     |							 |						     |
       |			     |					       min	 |					   min	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       R |						   A |
       |			     |						       s |						   s |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       R |						   A |
       |			     |						       d |						   d |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |			       </div>		     |
       |			     |				   <div>		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Gr		 |						     |
       |			     |					   =		 |						     |
       |			     |							 |						     |
       |			     |					       min	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       G |						     |
       |			     |						       s |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       G |						     |
       |			     |						       d |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |						     |
       |			     |				   <div>		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Br		 |						     |
       |			     |					   =		 |						     |
       |			     |							 |						     |
       |			     |					       min	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       B |						     |
       |			     |						       s |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       B |						     |
       |			     |						       d |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |						     |
       +-----------------------------+---------------------------------------------------+---------------------------------------------------+
       |GL_MAX			     | <div>						 | <div>					     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Rr		 |				       Ar	     |
       |			     |					   =		 |				       =	     |
       |			     |							 |						     |
       |			     |					       max	 |					   max	     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       R |						   A |
       |			     |						       s |						   s |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       R |						   A |
       |			     |						       d |						   d |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |			       </div>		     |
       |			     |				   <div>		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Gr		 |						     |
       |			     |					   =		 |						     |
       |			     |							 |						     |
       |			     |					       max	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       G |						     |
       |			     |						       s |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       G |						     |
       |			     |						       d |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |						     |
       |			     |				   <div>		 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |					   Br		 |						     |
       |			     |					   =		 |						     |
       |			     |							 |						     |
       |			     |					       max	 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       B |						     |
       |			     |						       s |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |						       B |						     |
       |			     |						       d |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |							 |						     |
       |			     |				   </div>		 |						     |
       +-----------------------------+---------------------------------------------------+---------------------------------------------------+

       The results of these equations are clamped to the range 0 1.

       The GL_MIN and GL_MAX equations are useful for applications that analyze image data (image thresholding against a constant color, for
       example). The GL_FUNC_ADD equation is useful for antialiasing and transparency, among other things.

       Initially, both the RGB blend equation and the alpha blend equation are set to GL_FUNC_ADD.

NOTES

       The GL_MIN, and GL_MAX equations do not use the source or destination factors, only the source and destination colors.

ERRORS

       GL_INVALID_ENUM is generated if mode is not one of GL_FUNC_ADD, GL_FUNC_SUBTRACT, GL_FUNC_REVERSE_SUBTRACT, GL_MAX, or GL_MIN.

       GL_INVALID_VALUE is generated by glBlendEquationi if buf is greater than or equal to the value of GL_MAX_DRAW_BUFFERS.

ASSOCIATED GETS

       glGet() with an argument of GL_BLEND_EQUATION_RGB

       glGet() with an argument of GL_BLEND_EQUATION_ALPHA

SEE ALSO

       glBlendColor(), glBlendFunc()glBlendFuncSeparate()

COPYRIGHT

       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014						       GLBLENDEQUATION(3G)
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