1 files changed, 68 insertions, 0 deletions
diff --git a/examples/shellmath/faster_e_demo.sh b/examples/shellmath/faster_e_demo.sh
new file mode 100644
index 0000000..84558a2
--- /dev/null
+++ b/examples/shellmath/faster_e_demo.sh
@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+
+###############################################################################
+# This script performs the same task as "slower_e_demo.sh" but with a major
+# performance optimization. The speedup is especially noticeable on GNU
+# emulation layers for Windows such as Cygwin and minGW, where the overhead
+# of subshelling is quite significant.
+#
+# The speedup uses global storage space to simulate pass-and-return by
+# reference so that you can capture the side effects of a function call without
+# writing to stdout and wrapping the call in a subshell. How to use:
+#
+#    Turn on  "__shellmath_isOptimized"  as shown below.
+#    Then instead of invoking  "mySum = $(_shellmath_add  $x  $y)",
+#    call  "_shellmath_add  $x  $y;  _shellmath_getReturnValue  mySum".
+###############################################################################
+
+source shellmath.sh
+
+# Setting the '-t' flag will cause the script to time the algorithm
+if [[ "$1" == '-t' ]]; then
+    do_timing=${__shellmath_true}
+    shift
+fi
+
+if [[ $# -ne 1 ]]; then
+    echo "USAGE: ${BASH_SOURCE##*/}  [-t]  *N*"
+    echo "       Approximates 'e' using the N-th order Maclaurin polynomial"
+    echo "       (i.e. the Taylor polynomial centered at 0)."
+    echo "       Specify the '-t' flag to time the main algorithm."
+    exit 0
+elif [[ ! "$1" =~ ^[0-9]+$ ]]; then
+    echo "Illegal argument. Whole numbers only, please."
+    exit 1
+fi
+
+__shellmath_isOptimized=${__shellmath_true}
+
+
+function run_algorithm()
+{
+    # Initialize
+    n=0;  N=$1;  zero_factorial=1
+
+    # Initialize "e" to its zeroth-order term
+    _shellmath_divide  1  $zero_factorial
+    _shellmath_getReturnValue term
+    e=$term
+
+    # Compute successive terms T(n) := T(n-1)/n and accumulate into e
+    for ((n=1; n<=N; n++)); do
+        _shellmath_divide  "$term"  "$n"
+        _shellmath_getReturnValue term
+        _shellmath_add  "$e"  "$term"
+        _shellmath_getReturnValue e
+    done
+
+    echo "e = $e"
+}
+
+if (( do_timing == __shellmath_true )); then
+    time run_algorithm "$1"
+else
+    run_algorithm "$1"
+fi
+
+exit 0
+