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==sfadd== {| class="wikitable" align="center" cellspacing="0" border="1" ! colspan="4" style="background:#ffdead;" | Add, multiply, or divide RSF datasets. |- ! colspan="4" | sfadd > out.rsf scale= add= sqrt= abs= log= exp= mode= [< file0.rsf] file1.rsf file2.rsf ... |- | colspan="4" | The various operations, if selected, occur in the following order:<br><br>(1) Take absolute value, abs=<br>(2) Add a scalar, add=<br>(3) Take the natural logarithm, log=<br>(4) Take the square root, sqrt=<br>(5) Multiply by a scalar, scale=<br>(6) Compute the base-e exponential, exp=<br>(7) Add, multiply, or divide the data sets, mode=<br><br>sfadd operates on integer, float, or complex data, but all the input<br>and output files must be of the same data type.<br><br>An alternative to sfadd is sfmath, which is more versatile, but may be<br>less efficient. |- | ''bools '' || '''abs=''' || || If true take absolute value [nin] |- | ''floats '' || '''add=''' || || Scalar values to add to each dataset [nin] |- | ''bools '' || '''exp=''' || || If true compute exponential [nin] |- | ''bools '' || '''log=''' || || If true take logarithm [nin] |- | ''string '' || '''mode=''' || || 'a' means add (default), <br> 'p' or 'm' means multiply, <br> 'd' means divide |- | ''floats '' || '''scale=''' || || Scalar values to multiply each dataset with [nin] |- | ''bools '' || '''sqrt=''' || || If true take square root [nin] |} <tt>sfadd</tt> is useful for combining (adding, dividing, or multiplying) several datasets. What if you want to subtract two datasets? Easy. Use the <tt>scale</tt> parameter as follows: <pre> bash$ sfadd data1.rsf data2.rsf scale=1,-1 > diff.rsf </pre> or <pre> bash$ sfadd < data1.rsf data2.rsf scale=1,-1 > diff.rsf </pre> The same task can be accomplished with the more general <tt>sfmath</tt> program: <pre> bash$ sfmath one=data1.rsf two=data2.rsf output='one-two' > diff.rsf </pre> or <pre> bash$ sfmath < data1.rsf two=data2.rsf output='input-two' > diff.rsf </pre> In both cases, the size and shape of <tt>data1.rsf</tt> and <tt>data2.rsf</tt> hypercubes should be the same, and a warning message is printed out if the the axis sampling parameters (such as <tt>o1</tt> or <tt>d1</tt>) in these files are different. ====Implementation: [https://github.com/ahay/src/blob/master/system/main/add.c system/main/add.c]==== The first input file is either in the list or in the standard input. <syntaxhighlight lang="c"> /* find number of input files */ if (isatty(fileno(stdin))) { /* no input file in stdin */ nin=0; } else { filename[0] = "in"; nin=1; } </syntaxhighlight> Collect input files in the <tt>in</tt> array from all command-line parameters that don't contain an "<tt>=</tt>" sign. The total number of input files is <tt>nin</tt>. <syntaxhighlight lang="c"> for (i=1; i< argc; i++) { /* collect inputs */ if (NULL != strchr(argv[i],'=')) continue; /* not a file */ filename[nin] = argv[i]; nin++; } if (0==nin) sf_error ("no input"); /* nin = no of input files*/ </syntaxhighlight> A helper function <tt>check_compat</tt> checks the compatibility of input files. <syntaxhighlight lang="c"> static void check_compat (sf_datatype type /* data type */, size_t nin /* number of files */, sf_file* in /* input files [nin] */, int dim /* file dimensionality */, const int* n /* dimensions [dim] */) /* Check that the input files are compatible. Issue error for type mismatch or size mismatch. Issue warning for grid parameters mismatch. */ { int ni, id; size_t i; float d, di, o, oi; char key[3]; const float tol=1.e-5; /* tolerance for comparison */ for (i=1; i < nin; i++) { if (sf_gettype(in[i]) != type) sf_error ("type mismatch: need %d",type); for (id=1; id <= dim; id++) { (void) snprintf(key,3,"n%d",id); if (!sf_histint(in[i],key,&ni) || ni != n[id-1]) sf_error("%s mismatch: need %d",key,n[id-1]); (void) snprintf(key,3,"d%d",id); if (sf_histfloat(in[0],key,&d)) { if (!sf_histfloat(in[i],key,&di) || (fabsf(di-d) > tol*fabsf(d))) sf_warning("%s mismatch: need %g",key,d); } else { d = 1.; } (void) snprintf(key,3,"o%d",id); if (sf_histfloat(in[0],key,&o) && (!sf_histfloat(in[i],key,&oi) || (fabsf(oi-o) > tol*fabsf(d)))) sf_warning("%s mismatch: need %g",key,o); } } } </syntaxhighlight> Finally, we enter the main loop, where the input data are getting read buffer by buffer and combined in the total product depending on the data type. <syntaxhighlight lang="c"> for (nbuf /= sf_esize(in[0]); nsiz > 0; nsiz -= nbuf) { if (nbuf > nsiz) nbuf=nsiz; for (j=0; j < nin; j++) { collect = (bool) (j != 0); switch(type) { case SF_FLOAT: sf_floatread((float*) bufi, nbuf, in[j]); add_float(collect, nbuf, (float*) buf, (const float*) bufi, cmode, scale[j], add[j], abs_flag[j], log_flag[j], sqrt_flag[j], exp_flag[j]); break; </syntaxhighlight> The data combination program for floating point numbers is <tt>add_float</tt>. <syntaxhighlight lang="c"> static void add_float (bool collect, /* if collect */ size_t nbuf, /* buffer size */ float* buf, /* output [nbuf] */ const float* bufi, /* input [nbuf] */ char cmode, /* operation */ float scale, /* scale factor */ float add, /* add factor */ bool abs_flag, /* if abs */ bool log_flag, /* if log */ bool sqrt_flag, /* if sqrt */ bool exp_flag /* if exp */) /* Add floating point numbers */ { size_t j; float f; for (j=0; j < nbuf; j++) { f = bufi[j]; if (abs_flag) f = fabsf(f); f += add; if (log_flag) f = logf(f); if (sqrt_flag) f = sqrtf(f); if (1. != scale) f *= scale; if (exp_flag) f = expf(f); if (collect) { switch (cmode) { case 'p': /* product */ case 'm': /* multiply */ buf[j] *= f; break; case 'd': /* delete */ if (f != 0.) buf[j] /= f; break; default: /* add */ buf[j] += f; break; } } else { buf[j] = f; } } } </syntaxhighlight>
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