Automatically finding E-series matches and metric prefixes

1 files changed, 82 insertions, 0 deletions

diff --git a/lace.rb b/lace.rb
index ef9a97e..b5aebf1 100644
--- a/lace.rb
+++ b/lace.rb
@@ -1,7 +1,89 @@
+require "bigdecimal"
 require "set"
 
 module Lace
 
+  PREFIXES = {
+    "femto" => 10**-15,
+    "f" => 10**-15,
+    "pico" => 10**-12,
+    "p" => 10**-12,
+    "nano" => 10**-9,
+    "n" => 10**-9,
+    "micro" => 10**-6,
+    "u" => 10**-6,
+    "µ" => 10**-6,
+    "milli" => 10**-3,
+    "m" => 10**-3,
+    "" => 10**0,
+    "kilo" => 10**3,
+    "k" => 10**3,
+    "mega" => 10**6,
+    "M" => 10**6,
+    }
+
+  def self.number(num)
+    num = num.to_s
+    PREFIXES.each do | p, d |
+      if num =~ /^(.+)#{p}$/i
+        begin
+          num = BigDecimal($1) * d
+          break
+        rescue ArgumentError
+        end
+      end
+    end
+    num = BigDecimal(num) unless num.instance_of?(BigDecimal)
+    return "0" if num == 0
+    prefix = "f"
+    div = PREFIXES["f"]
+    PREFIXES.each do | p, d |
+      if num.abs >= d and d >= div and (d > div or p.size < prefix.size or (p.size == prefix.size and p > prefix))
+        prefix = p
+        div = d
+      end
+    end
+    num /= div
+    num = num.to_s("F")
+    num.sub!(/\.0$/, "")
+    return "#{num}#{prefix}"
+  end
+
+  E3 = [10, 22, 47]
+  E6 = E3 + [15, 33, 68]
+  E12 = E6 + [12, 18, 27, 39, 56, 82]
+  E24 = E12 + [11, 13, 16, 20, 24, 30, 36, 43, 51, 62, 75, 91]
+
+  E48 = [100, 105, 110, 115, 121, 127, 133, 140, 147, 154, 162, 169, 178, 187, 196, 205, 215, 226, 237, 249, 261, 274, 287, 301, 316, 332, 348, 365, 383, 402, 422, 442, 464, 487, 511, 536, 562, 590, 619, 649, 681, 715, 750, 787, 825, 866, 909, 953]
+  E96 = E48 + [102, 107, 113, 118, 124, 130, 137, 143, 150, 158, 165, 174, 182, 191, 200, 210, 221, 232, 243, 255, 267, 280, 294, 309, 324, 340, 357, 374, 392, 412, 432, 453, 475, 499, 523, 549, 576, 604, 634, 665, 698, 732, 768, 806, 845, 887, 931, 976]
+  E192 = E96 + [101, 104, 106, 109, 111, 114, 117, 120, 123, 126, 129, 132, 135, 138, 142, 145, 149, 152, 156, 160, 164, 167, 172, 176, 180, 184, 189, 193, 198, 203, 208, 213, 218, 223, 229, 234, 240, 246, 252, 258, 264, 271, 277, 284, 291, 298, 305, 312, 320, 328, 336, 344, 352, 361, 370, 379, 388, 397, 407, 417, 427, 437, 448, 459, 470, 481, 493, 505, 517, 530, 542, 556, 569, 583, 597, 612, 626, 642, 657, 673, 690, 706, 723, 741, 759, 777, 796, 816, 835, 856, 876, 898, 920, 942, 965, 988]
+
+  def self.nearest(num, set)
+    return BigDecimal(0) if num == 0
+    base = set.min
+    exp = Math.log10(base).round
+    numexp = Math.log10(num).floor
+    num = num * 10**(exp-numexp)
+    candidate = nil
+    delta = Float::INFINITY
+    set.each do | c |
+      d = (num - c).abs
+      if d < delta
+        candidate = c
+        delta = d
+      end
+    end
+    return BigDecimal(candidate * 10**(numexp-exp), exp+1)
+  end
+
+  def self.e3(num); nearest(num, E3); end
+  def self.e6(num); nearest(num, E6); end
+  def self.e12(num); nearest(num, E12); end
+  def self.e24(num); nearest(num, E24); end
+  def self.e48(num); nearest(num, E48); end
+  def self.e96(num); nearest(num, E96); end
+  def self.e192(num); nearest(num, E192); end
+
   class Netlist
 
     attr_reader :components