Add Selection Sort in M4 (#4968)

Author: rzuckerm

archive/m/m4/selection-sort.m4

@@ -0,0 +1,93 @@
+divert(-1)
+define(`show_usage',
+`Usage: please provide a list of at least two integers to sort in the format "1, 2, 3, 4, 5"
+m4exit(`1')')
+
+dnl Reference: https://www.gnu.org/software/m4/manual/m4.html#index-array
+dnl array_get(var_name, idx)
+define(`array_get', `defn(format(``%s[%s]'', `$1', `$2'))')
+
+dnl array_set(var_name, idx, value)
+define(`array_set', `define(format(``%s[%s]'', `$1', `$2'), `$3')')
+
+dnl array_swap(var_name, idx1, idx2):
+dnl   t = var_name[idx1]
+dnl   var_name[idx1] = var_name[idx2]
+dnl   var_name[idx] = t
+define(`array_swap',
+`pushdef(`t', array_get(`$1', `$2'))dnl
+array_set(`$1', `$2', array_get(`$1', `$3'))dnl
+array_set(`$1', `$3', t)dnl
+popdef(`t')'dnl
+)
+
+dnl is_valid(n)
+define(`is_valid', `eval(regexp(`$1', `^\s*-?[0-9]+\s*$') >= 0)')
+
+dnl parse_int_list(varname, args):
+dnl   varname[length] = 0
+dnl   foreach arg in args:
+dnl     if not is_valid(arg):
+dnl       Return 0
+dnl     varname[varname[length]] = arg
+dnl     varname[length] = varname[length] + 1
+dnl   Return 1
+define(`parse_int_list',
+`array_set(`$1', `length', 0)dnl
+_parse_int_list(`$1', $2)'dnl
+)
+define(`_parse_int_list',
+`ifelse(is_valid(`$2'), 0, `0',
+`array_set(`$1', array_get(`$1', `length'), `$2')dnl
+array_set(`$1', `length', incr(array_get(`$1', `length')))dnl
+ifelse(eval($# > 2), 1, `_parse_int_list(`$1', shift(shift($@)))', `1')'dnl
+)'dnl
+)
+
+dnl show_int_list(varname):
+dnl   for i = 0 to n-1:
+dnl      if i > 0:
+dnl        Output ", "
+dnl      Output varname[i]
+define(`show_int_list', `_show_int_list(`$1', 0)')
+define(`_show_int_list',
+`ifelse(eval($2 < array_get(`$1', `length')), 1,
+`ifelse(eval($2 > 0), 1, `, ')dnl
+array_get(`$1', $2)`'dnl
+_show_int_list(`$1', incr($2))'`'dnl
+)'dnl
+)
+
+dnl Reference: https://en.wikipedia.org/wiki/Selection_sort#Implementations
+dnl selection_sort(varname):
+dnl   n = varname[length]
+dnl   for i = 0 to n-2:
+dnl     jmin = i
+dnl     for j = i+1 to n-1:
+dnl       if varname[j] < varname[jmin]:
+dnl         jmin = j
+dnl     if jmin != i:
+dnl       swap(varname, i, jmin)
+define(`selection_sort', `_selection_sort_outer(`$1', 0)')
+define(`_selection_sort_outer',
+`ifelse(eval($2 < decr(array_get(`$1', `length'))), 1,
+`_selection_sort_inner(`$1', `$2', incr($2), `$2')dnl
+_selection_sort_outer(`$1', incr($2))'dnl
+)'dnl
+)
+dnl varname=$1, i=$2, j=$3, jmin=$4
+define(`_selection_sort_inner',
+`ifelse(eval($3 >= array_get(`$1', `length')), 1,
+`ifelse(eval($4 != $2), 1, array_swap(`$1', `$2', `$4'))',
+`ifelse(eval(array_get(`$1', $3) < array_get(`$1', $4)), 1,
+`_selection_sort_inner(`$1', `$2', incr($3), `$3')',
+`_selection_sort_inner(`$1', `$2', incr($3), `$4')'dnl
+)'dnl
+)'dnl
+)
+
+divert(0)dnl
+ifelse(eval(ARGC < 1 || len(ARGV1) < 1 || !parse_int_list(`arr', ARGV1)), 1, `show_usage()')dnl
+ifelse(eval(array_get(`arr', `length') < 2), 1, `show_usage()')dnl
+selection_sort(`arr')dnl
+show_int_list(`arr')