feat: new macro (mp_md5) for calculating an md5 hash of a set of columns

base/mp_md5.sas

@@ -0,0 +1,58 @@
+/**
+  @file
+  @brief Generates an md5 expression for hashing a set of variables
+  @details This is the same algorithm used to hash records in
+  [Data Controller for SAS](https://datacontroller.io) (free for up
+  to 5 users).
+
+  It is not designed to be efficient - it is designed to be effective,
+  given the range of edge cases (large floating points, special missing
+  numerics, thousands of columns, very wide columns).
+
+  It can be used only in data step, eg as follows:
+
+      data _null_;
+        set sashelp.class;
+        hashvar=%mp_md5(cvars=name sex, nvars=age height weight);
+        put hashvar=;
+      run;
+
+  Unfortunately it will not run in SQL - it fails with the following message:
+
+  > The width value for HEX is out of bounds. It should be between 1 and 16
+
+  The macro will also cause errors if the data contains (non-special) missings
+  and the (undocumented) `options dsoptions=nonote2err;` is in effect.
+
+  This can be avoided in two ways:
+
+  @li Global option:  `options dsoptions=nonote2err;`
+  @li Data step option: `data YOURLIB.YOURDATASET /nonote2err;`
+
+  @param cvars= Space seperated list of character variables
+  @param nvars= Space seperated list of numeric variables
+
+  <h4> Related Programs </h4>
+  @li mp_init.sas
+
+  @version 9.2
+  @author Allan Bowe
+**/
+
+%macro mp_md5(cvars=,nvars=);
+%local i var sep;
+put(md5(
+  %do i=1 %to %sysfunc(countw(&cvars));
+    %let var=%scan(&cvars,&i,%str( ));
+    &sep put(md5(trim(&var)),$hex32.)
+    %let sep=!!;
+  %end;
+  %do i=1 %to %sysfunc(countw(&nvars));
+    %let var=%scan(&nvars,&i,%str( ));
+    /* multiply by 1 to strip precision errors (eg 0 != 0) */
+    /* but ONLY if not missing, else will lose any special missing values */
+    &sep put(md5(trim(put(ifn(missing(&var),&var,&var*1),binary64.))),$hex32.)
+    %let sep=!!;
+  %end;
+),hex32.)
+%mend mp_md5;