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	Add exercise: [▶02] Saturated subtraction - libzahl - big integer library
	git clone git://git.suckless.org/libzahl
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	---
	commit d89b4e54d7b4ee8aee05051ccf6e3b96019ac3ea
	parent dbb82e8a1184eaa7f6fa4b04e0560589cc6092e9
	Author: Mattias Andrée <[email protected]>
	Date: Sun, 24 Jul 2016 18:04:15 +0200

	Add exercise: [▶02] Saturated subtraction

	Signed-off-by: Mattias Andrée <[email protected]>

	Diffstat:
	M doc/exercises.tex \| 32 +++++++++++++++++++++++++++++…

	1 file changed, 31 insertions(+), 1 deletion(-)
	---
	diff --git a/doc/exercises.tex b/doc/exercises.tex
	@@ -22,6 +22,22 @@
	\begin{enumerate}[label=\textbf{\arabic*}.]


	+
	+\item {[$\RHD$\textit{02}]} \textbf{Saturated subtraction}
	+
	+Implement the function
	+
	+\vspace{-1em}
	+\begin{alltt}
	+ void monus(z_t r, z_t a, z_t b);
	+\end{alltt}
	+\vspace{-1em}
	+
	+\noindent
	+which calculates $a \dotminus b = \max \{ 0,~ a - b \}$.
	+
	+
	+
	\item {[\textit{M10}]} \textbf{Convergence of the Lucas Number ratios}

	Find an approximation for
	@@ -122,6 +138,20 @@ Use this to implement a fast primality tester.

	\begin{enumerate}[label=\textbf{\arabic*}.]

	+\item \textbf{Saturated subtraction}
	+
	+\vspace{-1em}
	+\begin{alltt}
	+void monus(z_t r, z_t a, z_t b)
	+\{
	+ zsub(r, a, b);
	+ if (zsignum(r) < 0)
	+ zsetu(r, 0);
	+\}
	+\end{alltt}
	+
	+
	+
	\item \textbf{Convergence of the Lucas Number ratios}

	It would be a mistake to use bignum, and bigint in particular,
	@@ -243,7 +273,7 @@ enum zprimality ptest_fast(z_t p)
	z_t a;
	int c = zcmpu(p, 2);
	if (c <= 0)
	- return c ? NONPRIME : PRIME;
	+ return c ? NONPRIME : PRIME;
	zinit(a);
	zsetu(a, 1);
	zlsh(a, a, p);