# Date: Sat, 02 Aug 2014 12:27:00 -0400

# To: bug-gawk@gnu.org

# From: Katherine Wasserman <katie@wass.net>

# Message-ID: <E1XDc9F-0007BX-O1@eggs.gnu.org>

# Subject: [bug-gawk] GAWK 4.1 SQRT() bug

# 

# In version 4.1.60 of GAWK the sqrt() function does not work correctly on bignums.

# Here's a demo of the problem along with, a function that does work correctly.

# 

# Running this program (sqrt-bug.awk):

# --------------------------------------------------------------------

@load "intdiv"

BEGIN {

a=11111111111111111111111111111111111111111111111111111111111

print sqrt(a^2)

#print sq_root(a^2)

# ADR: Added for gawk-4.1-stable which doesn't have built-in intdiv() function

if (PROCINFO["version"] < "4.1.60")

  print sq_root2(a^2)

else

  print sq_root(a^2)

}

function sq_root(x, temp,r,z)

{  temp=substr(x,1,length(x)/2) + 0 # a good first guess

   z=0

   while (abs(z-temp)>1)

    { z=temp

      intdiv(x,temp,r)

      temp=r["quotient"] + temp

      intdiv(temp,2,r)

      temp=r["quotient"]

    }

   return temp

}

function sq_root2(x, temp,r,z)

{  temp=substr(x,1,length(x)/2) + 0 # a good first guess

   z=0

   while (abs(z-temp)>1)

    { z=temp

      awk_div(x,temp,r)

      temp=r["quotient"] + temp

      awk_div(temp,2,r)

      temp=r["quotient"]

    }

   return temp

}

function abs(x)

{ return (x<0 ? -x : x)

}

# 

# --------------------------------------------------------------------

# gawk -M -f sqrt-bug.awk

# 

# results in:

# 11111111111111111261130863809439559987542611609749437808640

# 11111111111111111111111111111111111111111111111111111111111

# 

# Thanks,

# Katie

# 

# div --- do integer division

function awk_div(numerator, denominator, result,    i, save_PREC)

{

	save_PREC = PREC

	PREC = 400	# good enough for this test

	split("", result)

	numerator = int(numerator)

	denominator = int(denominator)

	result["quotient"] = int(numerator / denominator)

	result["remainder"] = int(numerator % denominator)

	PREC = save_PREC

	return 0.0

}