From 319f308b49786c9fcd3a77aa4f234df08eb2fc83 Mon Sep 17 00:00:00 2001
From: stderr64 <stderr64@null.net>
Date: Fri, 6 Feb 2026 21:53:12 +0200
Subject: Added experiment showing how to detect is integer positive or
 negative

---
 bit_test/Makefile            |  5 ++++
 bit_test/test_positive_int.c | 55 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 bit_test/Makefile
 create mode 100644 bit_test/test_positive_int.c

(limited to 'bit_test')

diff --git a/bit_test/Makefile b/bit_test/Makefile
new file mode 100644
index 0000000..d62bb86
--- /dev/null
+++ b/bit_test/Makefile
@@ -0,0 +1,5 @@
+CC=gcc
+CFLAGS=-O2 -mavx2 -Wall -Werror -pedantic -std=gnu23
+
+test_positive_int:
+	$(CC) ${CFLAGS} ./test_positive_int.c -o ./test_positive_int
diff --git a/bit_test/test_positive_int.c b/bit_test/test_positive_int.c
new file mode 100644
index 0000000..03d1bd0
--- /dev/null
+++ b/bit_test/test_positive_int.c
@@ -0,0 +1,55 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <string.h>
+
+bool is_int_positive( int test_int ){
+	/*
+		multiply test_int by 2 to get the amount of characters/bits
+		that would be in the hexadecimal value.
+		For example:
+		8-bit unsigned/signed = 1 * 2 = 2 (0x00 - 0xFF)
+		16-bit unsigned/signed = 2 * 2 = 4 (0x0000 - 0xFFFF)
+		32-bit unsigned/signed = 4 * 2 = 8 (0x00000000 - 0xFFFFFFFF)
+		64-bit unsigned/signed = 8 * 2 = 16 (0x0000000000000000 - 0xFFFFFFFFFFFFFFFF)
+	*/
+	size_t value_bits = sizeof(test_int) * 2;
+	/*
+		Next check if first bit is 1 (positive integer) or 0 (negative integer).
+		To do this the value bits must be used to right shift by the value bits count
+		so only the MSB is left.
+	*/
+	size_t value_bits_shift = test_int >> (value_bits - 1);
+	/*
+		Now do bitwise and operation to compare if the MSB is 1 (negative) or 0 (positive).
+		This works because the MSB tells if the integer contained in following bits should be taken
+		as positive or negative integer.
+		For positive integers the MSB is 0 and for negative integers the MSB is set to 1.
+		Because value_bits_shift was shifted right by value_bits minus 1 the result is
+		being left with just the bit containing the MSB value.
+		The bitwise and below checks if the MSB is not 1 then return true (positive integer) and otherwise false (negative integer).
+	*/
+	return (!(value_bits_shift & 0x1)) ? true : false;
+}
+
+int main( int argc, char **args ){
+	// Positive integer
+	int first_int = 12345;
+	// Negative integer
+	int second_int = -12345;
+	// Third integer that is just under 0
+	int third_int = -1;
+	// Fourth integer to test
+	int fourth_int = 1;
+	// Check the first integer
+	fprintf( stdout, "Result for positive integer: %i\n", is_int_positive(first_int) );
+	// Now do the same for the second one
+	fprintf( stdout, "Result for negative integer: %i\n", is_int_positive(second_int) );
+	// Third integer
+	fprintf( stdout, "Result for third integer that is -1: %i\n", is_int_positive(third_int) );
+	// Fourth integer
+	fprintf( stdout, "Result for fourth integer that is just positive by one: %i\n", is_int_positive(fourth_int) );
+	exit( EXIT_SUCCESS );
+}
-- 
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