Add math.factorial (#8298)

builtin/common/misc_helpers.lua

@@ -243,6 +243,20 @@ function math.sign(x, tolerance)
 	return 0
 end
 
+--------------------------------------------------------------------------------
+function math.factorial(x)
+	assert(x % 1 == 0 and x >= 0, "factorial expects a non-negative integer")
+	if x >= 171 then
+		-- 171! is greater than the biggest double, no need to calculate
+		return math.huge
+	end
+	local v = 1
+	for k = 2, x do
+		v = v * k
+	end
+	return v
+end
+
 --------------------------------------------------------------------------------
 function get_last_folder(text,count)
 	local parts = text:split(DIR_DELIM)

doc/lua_api.txt

@@ -2378,6 +2378,7 @@ Helper functions
     * tolerance: number, default: `0.0`
     * If the absolute value of `x` is within the `tolerance` or `x` is NaN,
       `0` is returned.
+* `math.factorial(x)`: returns the factorial of `x`
 * `string.split(str, separator, include_empty, max_splits, sep_is_pattern)`
     * `separator`: string, default: `","`
     * `include_empty`: boolean, default: `false`