commit abac38e6d6418ded518154cb15c3919d429a5ce0
Author: Juhani Krekelä <juhani@krekelä.fi>
Date:   Sat Aug 17 20:22:13 2019 +0300

    First commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..16f7a91
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+*.swp
+*.o
+plainhex
+plainunhex
diff --git a/CC0 b/CC0
new file mode 100644
index 0000000..670154e
--- /dev/null
+++ b/CC0
@@ -0,0 +1,116 @@
+CC0 1.0 Universal
+
+Statement of Purpose
+
+The laws of most jurisdictions throughout the world automatically confer
+exclusive Copyright and Related Rights (defined below) upon the creator and
+subsequent owner(s) (each and all, an "owner") of an original work of
+authorship and/or a database (each, a "Work").
+
+Certain owners wish to permanently relinquish those rights to a Work for the
+purpose of contributing to a commons of creative, cultural and scientific
+works ("Commons") that the public can reliably and without fear of later
+claims of infringement build upon, modify, incorporate in other works, reuse
+and redistribute as freely as possible in any form whatsoever and for any
+purposes, including without limitation commercial purposes. These owners may
+contribute to the Commons to promote the ideal of a free culture and the
+further production of creative, cultural and scientific works, or to gain
+reputation or greater distribution for their Work in part through the use and
+efforts of others.
+
+For these and/or other purposes and motivations, and without any expectation
+of additional consideration or compensation, the person associating CC0 with a
+Work (the "Affirmer"), to the extent that he or she is an owner of Copyright
+and Related Rights in the Work, voluntarily elects to apply CC0 to the Work
+and publicly distribute the Work under its terms, with knowledge of his or her
+Copyright and Related Rights in the Work and the meaning and intended legal
+effect of CC0 on those rights.
+
+1. Copyright and Related Rights. A Work made available under CC0 may be
+protected by copyright and related or neighboring rights ("Copyright and
+Related Rights"). Copyright and Related Rights include, but are not limited
+to, the following:
+
+  i. the right to reproduce, adapt, distribute, perform, display, communicate,
+  and translate a Work;
+
+  ii. moral rights retained by the original author(s) and/or performer(s);
+
+  iii. publicity and privacy rights pertaining to a person's image or likeness
+  depicted in a Work;
+
+  iv. rights protecting against unfair competition in regards to a Work,
+  subject to the limitations in paragraph 4(a), below;
+
+  v. rights protecting the extraction, dissemination, use and reuse of data in
+  a Work;
+
+  vi. database rights (such as those arising under Directive 96/9/EC of the
+  European Parliament and of the Council of 11 March 1996 on the legal
+  protection of databases, and under any national implementation thereof,
+  including any amended or successor version of such directive); and
+
+  vii. other similar, equivalent or corresponding rights throughout the world
+  based on applicable law or treaty, and any national implementations thereof.
+
+2. Waiver. To the greatest extent permitted by, but not in contravention of,
+applicable law, Affirmer hereby overtly, fully, permanently, irrevocably and
+unconditionally waives, abandons, and surrenders all of Affirmer's Copyright
+and Related Rights and associated claims and causes of action, whether now
+known or unknown (including existing as well as future claims and causes of
+action), in the Work (i) in all territories worldwide, (ii) for the maximum
+duration provided by applicable law or treaty (including future time
+extensions), (iii) in any current or future medium and for any number of
+copies, and (iv) for any purpose whatsoever, including without limitation
+commercial, advertising or promotional purposes (the "Waiver"). Affirmer makes
+the Waiver for the benefit of each member of the public at large and to the
+detriment of Affirmer's heirs and successors, fully intending that such Waiver
+shall not be subject to revocation, rescission, cancellation, termination, or
+any other legal or equitable action to disrupt the quiet enjoyment of the Work
+by the public as contemplated by Affirmer's express Statement of Purpose.
+
+3. Public License Fallback. Should any part of the Waiver for any reason be
+judged legally invalid or ineffective under applicable law, then the Waiver
+shall be preserved to the maximum extent permitted taking into account
+Affirmer's express Statement of Purpose. In addition, to the extent the Waiver
+is so judged Affirmer hereby grants to each affected person a royalty-free,
+non transferable, non sublicensable, non exclusive, irrevocable and
+unconditional license to exercise Affirmer's Copyright and Related Rights in
+the Work (i) in all territories worldwide, (ii) for the maximum duration
+provided by applicable law or treaty (including future time extensions), (iii)
+in any current or future medium and for any number of copies, and (iv) for any
+purpose whatsoever, including without limitation commercial, advertising or
+promotional purposes (the "License"). The License shall be deemed effective as
+of the date CC0 was applied by Affirmer to the Work. Should any part of the
+License for any reason be judged legally invalid or ineffective under
+applicable law, such partial invalidity or ineffectiveness shall not
+invalidate the remainder of the License, and in such case Affirmer hereby
+affirms that he or she will not (i) exercise any of his or her remaining
+Copyright and Related Rights in the Work or (ii) assert any associated claims
+and causes of action with respect to the Work, in either case contrary to
+Affirmer's express Statement of Purpose.
+
+4. Limitations and Disclaimers.
+
+  a. No trademark or patent rights held by Affirmer are waived, abandoned,
+  surrendered, licensed or otherwise affected by this document.
+
+  b. Affirmer offers the Work as-is and makes no representations or warranties
+  of any kind concerning the Work, express, implied, statutory or otherwise,
+  including without limitation warranties of title, merchantability, fitness
+  for a particular purpose, non infringement, or the absence of latent or
+  other defects, accuracy, or the present or absence of errors, whether or not
+  discoverable, all to the greatest extent permissible under applicable law.
+
+  c. Affirmer disclaims responsibility for clearing rights of other persons
+  that may apply to the Work or any use thereof, including without limitation
+  any person's Copyright and Related Rights in the Work. Further, Affirmer
+  disclaims responsibility for obtaining any necessary consents, permissions
+  or other rights required for any use of the Work.
+
+  d. Affirmer understands and acknowledges that Creative Commons is not a
+  party to this document and has no duty or obligation with respect to this
+  CC0 or use of the Work.
+
+For more information, please see
+<http://creativecommons.org/publicdomain/zero/1.0/>
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..3dfbf5e
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,36 @@
+DESTDIR ?=
+PREFIX ?= /usr/local
+EXEC_PREFIX ?= $(PREFIX)
+BINDIR ?= $(EXEC_PREFIX)/bin
+
+CFLAGS += -Os -g -Wall -Wextra -pedantic
+CPPFLAGS +=
+LDFLAGS +=
+
+BINS := plainhex plainunhex
+
+.SUFFIXES:
+.SUFFIXES: .c .o
+
+.PHONY: all install uninstall clean distclean
+
+all: $(BINS)
+
+plainhex: plainhex.o
+	$(CC) -o $@ $< $(LDFLAGS)
+
+plainunhex: plainunhex.o
+	$(CC) -o $@ $< $(LDFLAGS)
+.c.o:
+	$(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $<
+
+install: $(BINS)
+	install -D -m 755 -t '$(DESTDIR)$(BINDIR)' $(BINS)
+
+uninstall:
+	cd $(DESTDIR)$(BINDIR) && rm $(BINS)
+
+clean:
+	rm -f $(BINS) $(LIBEXECS) $(TOOLS) *.o
+
+distclean: clean
diff --git a/plainhex.c b/plainhex.c
new file mode 100644
index 0000000..69bb8a4
--- /dev/null
+++ b/plainhex.c
@@ -0,0 +1,38 @@
+#include <assert.h>
+#include <err.h>
+#include <stdio.h>
+
+char nybble(int n) {
+	assert(0 <= n && n <= 15);
+	return "0123456789abcdef"[n];
+}
+
+int main(void) {
+	for (;;) {
+		int byte = getchar();
+		if (byte == EOF) {
+			if (feof(stdin)) {
+				break;
+			} else {
+				err(1, "Error reading byte");
+			}
+		}
+
+		if (putchar(nybble(byte >> 4)) == EOF) {
+			err(1, "Error writing high nybble");
+		}
+		if (putchar(nybble(byte & 0xf)) == EOF) {
+			err(1, "Error writing low nybble");
+		}
+	}
+
+	if (putchar('\n') == EOF) {
+		err(1, "Error writing terminating newline");
+	}
+
+	if (fflush(stdout) == EOF) {
+		err(1, "Error flushing stdout");
+	}
+
+	return 0;
+}
diff --git a/plainunhex.c b/plainunhex.c
new file mode 100644
index 0000000..2b3e61d
--- /dev/null
+++ b/plainunhex.c
@@ -0,0 +1,70 @@
+#include <assert.h>
+#include <err.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+int nybble(char c) {
+	if ('0' <= c && c <= '9') {
+		return c - '0';
+	} else if ('A' <= c && c <= 'F') {
+		return c - 'A' + 10;
+	} else if ('a' <= c && c <= 'f') {
+		return c - 'a' + 10;
+	} else {
+		return -1;
+	}
+}
+
+int main(void) {
+	for (;;) {
+		int high_nybble;
+		bool eof_reached = false;
+		for (;;) {
+			char c = getchar();
+			if (c == EOF) {
+				if (feof(stdin)) {
+					eof_reached = true;
+					break;
+				} else {
+					err(1, "Error reading high nybble");
+				}
+			}
+
+			high_nybble = nybble(c);
+			if (high_nybble != -1) {
+				break;
+			}
+		}
+
+		if (eof_reached) {
+			break;
+		}
+
+		int low_nybble;
+		for (;;) {
+			char c = getchar();
+			if (c == EOF) {
+				if (feof(stdin)) {
+					errx(1, "Expected low nybble");
+				} else {
+					err(1, "Error reading low nybble");
+				}
+			}
+
+			low_nybble = nybble(c);
+			if (low_nybble != -1) {
+				break;
+			}
+		}
+
+		if (putchar((high_nybble << 4) | low_nybble) == EOF) {
+			err(1, "Error writing byte");
+		}
+	}
+
+	if (fflush(stdout) == EOF) {
+		err(1, "Error flushing stdout");
+	}
+
+	return 0;
+}