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	On sign manipulation - libzahl - big integer library
	git clone git://git.suckless.org/libzahl
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	---
	commit a70f79dfb22e8ea00231f5739f89ecc8d552643f
	parent 3a3ea3e654fa7131c0812977f92dc923d4daf9ce
	Author: Mattias Andrée <[email protected]>
	Date: Wed, 11 May 2016 22:26:27 +0200

	On sign manipulation

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

	Diffstat:
	M doc/arithmetic.tex \| 65 ++++++++++++++++++++++++++++-…

	1 file changed, 60 insertions(+), 5 deletions(-)
	---
	diff --git a/doc/arithmetic.tex b/doc/arithmetic.tex
	@@ -91,10 +91,10 @@ be detrimental to libzahl's simplicity.
	in-place operation:

	\begin{alltt}
	- zadd(a, a, b);
	- zadd(b, a, b); \textcolor{c}{/* \textrm{should be avoided} */}
	- zadd_unsigned(a, a, b);
	- zadd_unsigned(b, a, b); \textcolor{c}{/* \textrm{should be avoided} */}
	+ zadd(a, a, b);
	+ zadd(b, a, b); \textcolor{c}{/* \textrm{should be avoided} */}
	+ zadd_unsigned(a, a, b);
	+ zadd_unsigned(b, a, b); \textcolor{c}{/* \textrm{should be avoided} */}
	\end{alltt}

	\noindent
	@@ -137,4 +137,59 @@ TODO % zpow zpowu zmodpow zmodpowu
	\section{Sign manipulation}
	\label{sec:Sign manipulation}

	-TODO % zabs zneg
	+libzahl provides two functions for manipulating
	+the sign of integers:
	+
	+\begin{alltt}
	+ void zabs(z_t r, z_t a);
	+ void zneg(z_t r, z_t a);
	+\end{alltt}
	+
	+{\tt zabs} stores the absolute value of {\tt a}
	+in {\tt r}, that is, it creates a copy of
	+{\tt a} to {\tt r}, unless {\tt a} and {\tt r}
	+are the same reference, and then removes its sign;
	+if the value is negative, it becomes positive.
	+
	+\vspace{1em}
	+\(
	+ r \gets \lvert a \rvert =
	+ \left \lbrace \begin{array}{rl}
	+ -a & \quad \textrm{if}~a \le 0 \\
	+ +a & \quad \textrm{if}~a \ge 0 \\
	+ \end{array} \right .
	+\)
	+\vspace{1em}
	+
	+{\tt zneg} stores the negated of {\tt a}
	+in {\tt r}, that is, it creates a copy of
	+{\tt a} to {\tt r}, unless {\tt a} and {\tt r}
	+are the same reference, and then flips sign;
	+if the value is negative, it becomes positive,
	+if the value is positive, it becomes negative.
	+
	+\vspace{1em}
	+\(
	+ r \gets -a
	+\)
	+\vspace{1em}
	+
	+Note that there is no function for
	+
	+\vspace{1em}
	+\(
	+ r \gets -\lvert a \rvert =
	+ \left \lbrace \begin{array}{rl}
	+ a & \quad \textrm{if}~a \le 0 \\
	+ -a & \quad \textrm{if}~a \ge 0 \\
	+ \end{array} \right .
	+\)
	+\vspace{1em}
	+
	+\noindent
	+calling {\tt zabs} followed by {\tt zneg}
	+should be sufficient for most users:
	+
	+\begin{alltt}
	+ #define my_negabs(r, a) (zabs(r, a), zneg(r, r))
	+\end{alltt}