two/three-argument round, ceil, floor, trunk, signif

Some two-argument examples:

    julia> round(123.456, 1)
    100.0

    julia> round(123.456, 2)
    120.0

    julia> round(123.456, 3)
    123.0

    julia> round(123.456, 7)
    123.456

    julia> round(123.456, 4)
    123.5

    julia> round(-123.456, 4)
    -123.5

    julia> floor(123.456, 4)
    123.4

    julia> floor(-123.456, 4)
    -123.5

    julia> ceil(123.456, 4)
    123.5

    julia> ceil(-123.456, 4)
    -123.4

    julia> trunc(123.456, 4)
    123.4

    julia> trunc(-123.456, 4)
    -123.4

base/export.jl

@@ -473,6 +473,7 @@ export
     sign,
     signbit,
     signed,
+    signif,
     significand,
     sin,
     sinc,

base/floatfuncs.jl

@@ -57,3 +57,38 @@ end
 @vectorize_1arg Real isnan
 @vectorize_1arg Real isinf
 @vectorize_1arg Real isfinite
+
+# adapted from Matlab File Exchange roundsd: http://www.mathworks.com/matlabcentral/fileexchange/26212
+# for round, og is the power of 10 relative to the decimal point
+# for signif, og is the absolute power of 10
+# digits and base must be integers, x must be convertable to float
+
+function _signif_og(x, digits, base)
+    if base == 10
+        10. ^ floor(log10(abs(x)) - digits + 1.)
+    elseif base == 2
+        2. ^ floor(log2(abs(x)) - digits + 1.)
+    else
+        float(base) ^ floor(log2(abs(x))/log2(base) - digits + 1.)
+    end
+end
+_round_og(digits, base) = float(base) ^ (- digits)
+
+function signif(x, digits::Integer, base::Integer)
+    if digits < 0
+        throw(DomainError())
+    end
+    og = _signif_og(float(x), digits, base)
+    round(float(x)/og) * og
+end
+signif(x, digits) = signif(x, digits, 10)
+
+for f in (:round, :ceil, :floor, :trunc)
+    @eval begin
+        function ($f)(x, digits::Integer, base::Integer)
+            og = _round_og(digits, base)
+            ($f)(float(x) / og) * og
+        end
+        ($f)(x, digits) = ($f)(x, digits, 10)
+    end
+end