From cd73fd40ffc04a65abe0260fe82949d7c354e282 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sun, 2 Mar 2025 12:18:34 -0500
Subject: add inHG pressure unit

---
 test.c          |  2 ++
 test.h          |  2 ++
 test_pressure.c | 10 ++++++++++
 ui.c            |  6 +++---
 unit.c          | 10 ++++++++++
 unit.h          |  2 ++
 6 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/test.c b/test.c
index 72952f5..117f112 100644
--- a/test.c
+++ b/test.c
@@ -17,11 +17,13 @@ main(void) {
 	test_kilopascal();
 	test_bar();
 	test_psi();
+	test_inch_mercury();
 	test_as_pascal();
 	test_as_millibar();
 	test_as_kilopascal();
 	test_as_bar();
 	test_as_psi();
+	test_as_inch_mercury();
 
 	test_kelvin();
 	test_celsius();
diff --git a/test.h b/test.h
index 4f14ef8..86d59c0 100644
--- a/test.h
+++ b/test.h
@@ -23,11 +23,13 @@ void test_millibar(void);
 void test_kilopascal(void);
 void test_bar(void);
 void test_psi(void);
+void test_inch_mercury(void);
 void test_as_pascal(void);
 void test_as_millibar(void);
 void test_as_kilopascal(void);
 void test_as_bar(void);
 void test_as_psi(void);
+void test_as_inch_mercury(void);
 
 void test_kelvin(void);
 void test_celsius(void);
diff --git a/test_pressure.c b/test_pressure.c
index f04a1bc..e805858 100644
--- a/test_pressure.c
+++ b/test_pressure.c
@@ -29,6 +29,11 @@ test_psi(void) {
 	test(psi(123.456), 851199.15638539323);
 }
 
+void
+test_inch_mercury(void) {
+	test(inch_mercury(123.456), 418070.040384);
+}
+
 void
 test_as_pascal(void) {
 	test(as_pascal(pascal(123.456)), 123.456);
@@ -53,3 +58,8 @@ void
 test_as_psi(void) {
 	test(as_psi(psi(123.456)), 123.456);
 }
+
+void
+test_as_inch_mercury(void) {
+	test(as_inch_mercury(inch_mercury(123.456)), 123.456);
+}
diff --git a/ui.c b/ui.c
index cf97462..50b2f3f 100644
--- a/ui.c
+++ b/ui.c
@@ -37,12 +37,12 @@ static const TemperatureReader temperature_readers[nelem(temperature_units)] = {
 	as_celsius, as_kelvin, as_fahrenheit, as_rankine,
 };
 
-static const char *const pressure_units[] = {"mbar", "kPa", "bar", "psi"};
+static const char *const pressure_units[] = {"mbar", "kPa", "bar", "psi", "inHG"};
 static const PressureMaker pressure_makers[nelem(pressure_units)] = {
-	millibar, kilopascal, bar, psi,
+	millibar, kilopascal, bar, psi, inch_mercury,
 };
 static const PressureReader pressure_readers[nelem(pressure_units)] = {
-	as_millibar, as_kilopascal, as_bar, as_psi,
+	as_millibar, as_kilopascal, as_bar, as_psi, as_inch_mercury,
 };
 
 static const char *const volume_flow_rate_units[] = {"m³/s", "CFM"};
diff --git a/unit.c b/unit.c
index d1e487d..dfe75c4 100644
--- a/unit.c
+++ b/unit.c
@@ -85,6 +85,11 @@ psi(double x) {
 	return x * KG_PER_LB * G / pow(M_PER_IN, 2);
 }
 
+Pressure
+inch_mercury(double x) {
+	return x * 3386.389;
+}
+
 double
 as_pascal(Pressure x) {
 	return x;
@@ -110,6 +115,11 @@ as_psi(Pressure x) {
 	return x * pow(M_PER_IN, 2) / (KG_PER_LB * G);
 }
 
+double
+as_inch_mercury(Pressure x) {
+	return x / 3386.389;
+}
+
 
 Temperature
 kelvin(double x) {
diff --git a/unit.h b/unit.h
index 4e22a35..520285b 100644
--- a/unit.h
+++ b/unit.h
@@ -27,11 +27,13 @@ Pressure millibar(double x);
 Pressure kilopascal(double x);
 Pressure bar(double x);
 Pressure psi(double x);
+Pressure inch_mercury(double x);
 double as_pascal(Pressure x);
 double as_millibar(Pressure x);
 double as_kilopascal(Pressure x);
 double as_bar(Pressure x);
 double as_psi(Pressure x);
+double as_inch_mercury(Pressure x);
 
 
 typedef double Temperature;
-- 
cgit v1.2.3