replace awk with a more efficient built-ins-only algo

Index: strings.subr
===================================================================
--- strings.subr        (revision 294669)
+++ strings.subr        (working copy)
@@ -70,17 +70,63 @@ f_substr()
 #
 f_snprintf()
 {
+   local __funcname=f_snprintf
    local __var_to_set="$1" __size="$2"
    shift 2 # var_to_set size
-   eval "$__var_to_set"=\$\( printf -- \"\$@\" \| \
-       awk -v max=\"\$__size\" \''
-   {
-       len = length($0)
-       max -= len
-       print substr($0,0,(max > 0 ? len : max + len))
-       if ( max < 0 ) exit
-       max--
-   }'\' \)
+
+   if [ "$__size" -eq 0 ] 2> /dev/null; then
+       setvar "$__var_to_set" ""
+       return ${SUCCESS:-0}
+   elif [ $? -ge 2 ] || [ $__size -lt 0 ]; then
+       setvar "$__var_to_set" ""
+       echo "$__funcname: invalid size argument \`__size'" >&2
+       return ${FAILURE:-1}
+   fi
+
+   local __f_snprintf_tmp
+   f_sprintf __f_snprintf_tmp "$@"
+
+   local __tmp_size=${#__f_snprintf_tmp}
+   local __trim=$(( $__tmp_size - $__size )) __trimq
+   local __tbuf __tbuf_len
+   local __mask __mask_len
+   while [ $__trim -gt 0 ]; do
+       __tbuf="?"
+       __tbuf_len=1
+       if [ $__trim -le $__size ]; then
+           while [ $__tbuf_len -lt $(( $__trim / $__tbuf_len )) ]
+           do
+               __tbuf="$__tbuf?"
+               __tbuf_len=$(( $__tbuf_len + 1 ))
+           done
+           __trimq=$(( $__trim / $__tbuf_len ))
+           __trim=$(( $__trim - $__tbuf_len * $__trimq ))
+           while [ $__trimq -gt 0 ]; do
+               __f_snprintf_tmp="${__f_snprintf_tmp%$__tbuf}"
+               __trimq=$(( $__trimq - 1 ))
+           done
+       else
+           __mask="$__f_snprintf_tmp"
+           while [ $__tbuf_len -lt $(( $__size / $__tbuf_len )) ]
+           do
+               __tbuf="$__tbuf?"
+               __tbuf_len=$(( $__tbuf_len + 1 ))
+           done
+           __trimq=$(( $__size / $__tbuf_len ))
+           if [ $(( $__trimq * $__tbuf_len )) -ne $__size ]; then
+               __tbuf="$__tbuf?"
+               __tbuf_len=$(( $__tbuf_len + 1 ))
+           fi
+           __mask_len=$(( $__tmp_size - $__tbuf_len * $__trimq ))
+           __trim=$(( $__tmp_size - $__mask_len - $__size ))
+           while [ $__trimq -gt 0 ]; do
+               __mask="${__mask#$__tbuf}"
+               __trimq=$(( $__trimq - 1 ))
+           done
+           __f_snprintf_tmp="${__f_snprintf_tmp%"$__mask"}"
+       fi
+   done
+   setvar "$__var_to_set" "$__f_snprintf_tmp"
 }

 # f_sprintf $var_to_set $format [$arguments ...]