Retro-ification Fragment Shader

main.cpp

#include <SFML/Graphics.hpp>
#include <SFML/Window.hpp>
#include <SFML/System.hpp>

#include <iostream>
#include <string>
#include <memory>
#include <cmath>

constexpr sf::Uint8 ColorFloatToU8(float val) {
	return static_cast<sf::Uint8>(255.0f * val);
}

sf::Color ColorFromHSV(float hue, float sat, float val, float alpha=1.0f) {
	int i;
	float f, p, q, t;
	sf::Uint8 a = ColorFloatToU8(alpha);
	sf::Uint8 r,g,b;

	if(sat == 0) {
		r = g = b = ColorFloatToU8(val);
		return sf::Color(r, g, b, a);
	}

	hue *= 6.0;
	hue = std::fmod(hue, 6.0f);
	i = std::floor(hue);

	f = hue - i;
	p = val * (1 - sat);
	q = val * (1 - sat * f);
	t = val * (1 - sat * (1 - f));

	switch(i) {
	case 0:
		r = ColorFloatToU8(val);
		g = ColorFloatToU8(t);
		b = ColorFloatToU8(p);
		break;
	case 1:
		r = ColorFloatToU8(q);
		g = ColorFloatToU8(val);
		b = ColorFloatToU8(p);
		break;
	case 2:
		r = ColorFloatToU8(p);
		g = ColorFloatToU8(val);
		b = ColorFloatToU8(t);
		break;
	case 3:
		r = ColorFloatToU8(p);
		g = ColorFloatToU8(q);
		b = ColorFloatToU8(val);
		break;
	case 4:
		r = ColorFloatToU8(t);
		g = ColorFloatToU8(p);
		b = ColorFloatToU8(val);
		break;
	default:
		r = ColorFloatToU8(val);
		g = ColorFloatToU8(p);
		b = ColorFloatToU8(q);
	}

	return sf::Color(r, g, b, a);
}

int main() {
	std::cout << "Creating RenderWindow\n";
	sf::RenderWindow window(
		sf::VideoMode(800, 600),
		"SFML window",
		sf::Style::Close,
		sf::ContextSettings(0, 0, 0, 4, 4, sf::ContextSettings::Default)
	);

	std::cout << "Loading Shader\n";
	sf::Shader shader;
	
	// vvv ATTENTION: This is where the glsl shader is failing to compile! vvv
	if(!shader.loadFromFile("retro-frag.glsl", sf::Shader::Fragment)) {
		std::cerr << "ERROR: Unable to load shader!\n";
		return 1;
	}

	std::cout << "Creating Image : ";
	sf::Image img;
	img.create(256, 256, sf::Color(255, 255, 255));

	for(unsigned int j = 0; j < 256; ++j) {
		for(unsigned int i = 0; i < 256; ++i) {
			img.setPixel(i, j,
					ColorFromHSV(
							i / 255.0f,
							j / 255.0f,
							1.0f));
		}
	}

	std::cout << "Creating Texture\n"; std::cout.flush();
	sf::Texture tex;
	tex.loadFromImage(img);
	sf::Texture tex2;
	tex2.loadFromImage(img);

	std::cout << "Creating Sprites\n"; std::cout.flush();
	sf::Sprite sprite(tex);
	sf::Sprite sprite2(tex2);
	sprite2.setPosition(400, 0);
	shader.setUniform("texture", sf::Shader::CurrentTexture);
	shader.setUniform("bit_precision", sf::Glsl::Vec3(3, 3, 2));

	std::cout << "Starting Game Loop\n"; std::cout.flush();
	while(window.isOpen()) {
		sf::Event event;
		while(window.pollEvent(event)) {
			if(event.type == sf::Event::Closed)
				window.close();
		}

		window.clear(sf::Color::Green);
		window.draw(sprite);
		window.draw(sprite2, &shader);
		window.display();
	}

	return 0;
}

retro-frag.glsl

#version 440 compatibility

uniform sampler2D texture;
uniform ivec3 bit_precision; // A syntax error happens on this line for some reason

void main() {
    vec3 prec_fac = vec3(float(1 << bit_precision.x), float(1 << bit_precision.y), float(1 << bit_precision.z));
    vec3 factor_adjust = 1.0f / (prec_fac - 1.0f);
    vec4 color = texture2D(texture, gl_TexCoord[0].xy);
    vec4 low_color = vec4(
        floor(color.x * (prec_fac.x + 0.01f)) * factor_adjust.x,
        floor(color.y * (prec_fac.y + 0.01f)) * factor_adjust.y,
        floor(color.z * (prec_fac.z + 0.01f)) * factor_adjust.z,
        1.0f);
    
    gl_FragColor = low_color;
}

For some reason I'm getting a syntax error when trying to compile this shader.

Exact error:

Failed to compile fragment shader:
Fragment shader failed to compile with the following errors:
ERROR: 0:4: error(#132) Syntax error: ERROR: error(#273) 1 compilation errors.  No code generated

Edit:

Associated stackoverflow question: http://stackoverflow.com/q/39176620/2186002

Edit 2:

FIXED!!!

Here's the output of the provided main.cpp: