Use common prec validation also in BigDecimal#sqrt

Author: tompng

lib/bigdecimal.rb

@@ -146,12 +146,12 @@ def power(y, prec = nil)
   # Result has at least prec significant digits.
   #
   def sqrt(prec)
+    BigMath._validate_prec(prec, :sqrt, accept_zero: true)
     if infinite? == 1
       exception_mode = BigDecimal.mode(BigDecimal::EXCEPTION_ALL)
       raise FloatDomainError, "Computation results in 'Infinity'" if exception_mode.anybits?(BigDecimal::EXCEPTION_INFINITY)
       return INFINITY
     end
-    raise ArgumentError, 'negative precision' if prec < 0
     raise FloatDomainError, 'sqrt of negative value' if self < 0
     raise FloatDomainError, "sqrt of 'NaN'(Not a Number)" if nan?
     return self if zero?
@@ -190,9 +190,13 @@ def self._coerce_to_bigdecimal(x, method_name, complex_domain_error = false) # :
     raise ArgumentError, "#{x.inspect} can't be coerced into BigDecimal"
   end
 
-  def self._validate_prec(prec, method_name) # :nodoc:
+  def self._validate_prec(prec, method_name, accept_zero: false) # :nodoc:
     raise ArgumentError, 'precision must be an Integer' unless Integer === prec
-    raise ArgumentError, "Zero or negative precision for #{method_name}" if prec <= 0
+    if accept_zero
+      raise ArgumentError, "Negative precision for #{method_name}" if prec < 0
+    else
+      raise ArgumentError, "Zero or negative precision for #{method_name}" if prec <= 0
+    end
   end
 
   def self._infinity_computation_result # :nodoc: