ENH simplify formatting math

src/format.lua

@@ -2,6 +2,7 @@ local M = {}
 
 local __tostring		= tostring
 local __math_floor 		= math.floor
+local __math_log 		= math.log
 local __math_ceil 		= math.ceil
 local __string_format 	= string.format
 
@@ -23,21 +24,18 @@ M.round_to_string = function(x, places)
     end
 end
 
+-- ASSUME domain is (0, inf)
 M.precision_round_to_string = function(x, sig_fig)
-	sig_fig = sig_fig or 4
+   local adj = x == 0 and 1 or __math_floor(__math_log(x, 10)) + 1
-	if     x < 10   then return M.round_to_string(x, sig_fig - 1)
+   return M.round_to_string(x, (sig_fig or 4) - adj)
-	elseif x < 100  then return M.round_to_string(x, sig_fig - 2)
-	elseif x < 1000 then return M.round_to_string(x, sig_fig - 3)
-	else                 return M.round_to_string(x, sig_fig - 4)
-	end
 end
 
+local PREFIXES = {'', 'Ki', 'Mi', 'Gi', 'Ti', 'Pi'}
+
+-- ASSUME domain is (0, inf)
 M.convert_data_val = function(x)
-	if     	x < 1024       then	return '', x
+   local z = x == 0 and 0 or __math_floor(__math_log(x, 2) / 10)
-	elseif 	x < 1048576    then	return 'Ki', x / 1024
+   return PREFIXES[z + 1], x / 2 ^ (10 * z)
-	elseif 	x < 1073741824 then	return 'Mi', x / 1048576
-    else					    return 'Gi', x / 1073741824
-    end
 end
 
 return M