#!/usr/bin/env zsh

# @(#) s1       Demonstrate floating point arithmetic, zsh, bc.

echo
set +o nounset
LC_ALL=C ; LANG=C ; export LC_ALL LANG
echo "Environment: LC_ALL = $LC_ALL, LANG = $LANG"
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version "=o" $(_eat $0 $1) bc
set -o nounset

# set test3 = (4.985e-10 5.130e-10 5.486e-10 6.023e-10 7.015e-10)
# set test4 = (4.869e-10 5.010-10 5.363e-10 5.895e-10 6.887e-10)
# set test5 = $test3 - $test4

float difference test3 test4
echo
echo " Results of zsh built-in floating-point arithmetic:"
test3=(4.985e-10 5.130e-10 5.486e-10 6.023e-10 7.015e-10)
echo " test3 is $test3"
echo " test3[0] is ${test3[0]}"
echo " test3[1] is ${test3[1]}"
test4=(4.869e-10 5.010-10 5.363e-10 5.895e-10 6.887e-10)
echo " test4 is $test4"
echo " test4[2] is ${test4[2]}"

echo
for ((i=1 ; i<=${#test3} ; i++ ))
do
  (( difference = ${test3[$i]}-${test4[$i]} ))
  printf " difference $i of ${test3[$i]} ${test4[$i]} is %e\n" $difference
done

echo
echo " Results from bc, \"e\" format, expect error:"
t3=${test3[1]}
t4=${test4[1]}
echo "scale=4 ; $t3 - $t4" | tee t1 | bc
echo " input was:"
cat t1

echo
echo " Results from bc, format of bc:"
t3="4.985*10^-10"
t4="4.869*10^-10"
echo "scale=15 ; $t3 - $t4" | tee t1 | bc
echo " input was:"
cat t1

exit 0

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.11-x1, i686
Distribution        : Xandros Desktop 3.0.3 Business
zsh 4.2.4
bc 1.06

 Results of zsh built-in floating-point arithmetic:
 test3 is 4.985e-10 5.130e-10 5.486e-10 6.023e-10 7.015e-10
 test3[0] is 4.985e-10
 test3[1] is 4.985e-10
 test4 is 4.869e-10 5.010-10 5.363e-10 5.895e-10 6.887e-10
 test4[2] is 5.010-10

 difference 1 of 4.985e-10 4.869e-10 is 1.160000e-11
 difference 2 of 5.130e-10 5.010-10 is -1.501000e+01
 difference 3 of 5.486e-10 5.363e-10 is 1.230000e-11
 difference 4 of 6.023e-10 5.895e-10 is 1.280000e-11
 difference 5 of 7.015e-10 6.887e-10 is 1.280000e-11

 Results from bc, "e" format, expect error:
(standard_in) 1: parse error
(standard_in) 1: parse error
 input was:
scale=4 ; 4.985e-10 - 4.869e-10

 Results from bc, format of bc:
.000000000011600
 input was:
scale=15 ; 4.985*10^-10 - 4.869*10^-10