Initial data commit

Task/Long-multiplication/UNIX-Shell/long-multiplication-1.sh

@@ -0,0 +1 @@
+multiply() { echo "$1 $2 * p" | dc; }

Task/Long-multiplication/UNIX-Shell/long-multiplication-2.sh

@@ -0,0 +1,43 @@
+add() { # arbitrary-precision addition
+  local a="$1" b="$2" sum= carry=0
+  if (( ${#a} < ${#b} )); then
+    local t="$a"
+    a="$b" b="$t"
+  fi
+
+  while (( ${#a} )); do
+    local -i d1="${a##${a%?}}" d2="10#0${b##${b%?}}" s=carry+d1+d2
+    sum="${s##${s%?}}$sum"
+    carry="10#0${s%?}"
+    a="${a%?}" b="${b%?}"
+  done
+  echo "$sum"
+}
+
+multiply() { # arbitrary-precision multiplication
+  local a="$1" b="$2" product=0
+  if (( ${#a} < ${#b} )); then
+    local t="$a"
+    a="$b" b="$t"
+  fi
+
+  local zeroes=
+  while (( ${#b} )); do
+    local m1="$a"
+    local m2="${b##${b%?}}"
+    local partial=$zeroes
+    local -i carry=0
+    while (( ${#m1} )); do
+      local -i d="${m1##${m1%?}}"
+      m1="${m1%?}"
+      local -i p=d*m2+carry
+      partial="${p##${p%?}}$partial"
+      carry="10#0${p%?}"
+    done
+    partial="${carry#0}$partial"
+    product="$(add "$product" "$partial")"
+    zeroes=0$zeroes
+    b="${b%?}"
+  done
+  echo "$product"
+}