From f26f6086ca85adddf1a92a88c55394ce7f6f77ff Mon Sep 17 00:00:00 2001
From: adrien <adrien@bouvais.lu>
Date: Thu, 23 Apr 2026 00:14:57 +0200
Subject: [PATCH] Added Imperial unit scales

---
 src/Scalar.zig | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++
 src/Scales.zig | 39 ++++++++++++++++++++++++++---------
 2 files changed, 84 insertions(+), 10 deletions(-)

diff --git a/src/Scalar.zig b/src/Scalar.zig
index 12a10f7..ecc35f6 100644
--- a/src/Scalar.zig
+++ b/src/Scalar.zig
@@ -749,6 +749,61 @@ test "add/sub bare number on dimensionless scalar" {
     try std.testing.expectEqual(7, c.value);
 }
 
+test "Imperial length scales" {
+    const Foot = Scalar(f64, .{ .L = 1 }, .{ .L = .ft });
+    const Meter = Scalar(f64, .{ .L = 1 }, .{});
+    const Inch = Scalar(f64, .{ .L = 1 }, .{ .L = .inch });
+    const CentiMeter = Scalar(f64, .{ .L = 1 }, .{ .L = .c });
+    const Mile = Scalar(f64, .{ .L = 1 }, .{ .L = .mi });
+    const KiloMeter = Scalar(f64, .{ .L = 1 }, .{ .L = .k });
+    const Yard = Scalar(f64, .{ .L = 1 }, .{ .L = .yd });
+
+    // 1 ft → 0.3048 m
+    const one_ft = Foot{ .value = 1.0 };
+    try std.testing.expectApproxEqAbs(0.3048, one_ft.to(Meter).value, 1e-9);
+
+    // 12 in → 1 ft
+    const twelve_in = Inch{ .value = 12.0 };
+    try std.testing.expectApproxEqAbs(1.0, twelve_in.to(Foot).value, 1e-9);
+
+    // 1 in → 2.54 cm
+    const one_in = Inch{ .value = 1.0 };
+    try std.testing.expectApproxEqAbs(2.54, one_in.to(CentiMeter).value, 1e-9);
+
+    // 1 mi → 1.609344 km
+    const one_mi = Mile{ .value = 1.0 };
+    try std.testing.expectApproxEqAbs(1.609344, one_mi.to(KiloMeter).value, 1e-9);
+
+    // 3 ft → 1 yd
+    const three_ft = Foot{ .value = 3.0 };
+    try std.testing.expectApproxEqAbs(1.0, three_ft.to(Yard).value, 1e-9);
+}
+
+test "Imperial mass scales" {
+    const Pound = Scalar(f64, .{ .M = 1 }, .{ .M = .lb });
+    const KiloGram = Scalar(f64, .{ .M = 1 }, .{ .M = .k });
+    const Ounce = Scalar(f64, .{ .M = 1 }, .{ .M = .oz });
+    const Stone = Scalar(f64, .{ .M = 1 }, .{ .M = .st });
+
+    // 1 lb → ~0.453592 kg
+    const one_lb = Pound{ .value = 1.0 };
+    try std.testing.expectApproxEqAbs(0.45359237, one_lb.to(KiloGram).value, 1e-6);
+
+    // 16 oz → 1 lb
+    const sixteen_oz = Ounce{ .value = 16.0 };
+    try std.testing.expectApproxEqAbs(1.0, sixteen_oz.to(Pound).value, 1e-6);
+
+    // 1 stone → 14 lb
+    const one_st = Stone{ .value = 1.0 };
+    try std.testing.expectApproxEqAbs(14.0, one_st.to(Pound).value, 1e-4);
+
+    // 2 lb + 8 oz → 2.5 lb
+    const two_lb = Pound{ .value = 2.0 };
+    const eight_oz = Ounce{ .value = 8.0 };
+    const total = two_lb.add(eight_oz).to(Pound);
+    try std.testing.expectApproxEqAbs(2.5, total.value, 1e-6);
+}
+
 test "comparisons with comptime_int on dimensionless scalar" {
     const DimLess = Scalar(i128, .{}, .{});
     const x = DimLess{ .value = 42 };
diff --git a/src/Scales.zig b/src/Scales.zig
index 0732f93..246565f 100644
--- a/src/Scales.zig
+++ b/src/Scales.zig
@@ -41,6 +41,18 @@ pub const UnitScale = enum(isize) {
     hour = 3_600,
     year = 31_536_000,
 
+    // Imperial Length (Literal factors in meters)
+    // 1 inch = 0.0254 meters. Since enum backing is isize,
+    // we use a unique tag and handle the float in getFactor.
+    inch = -1001,
+    ft = -1002,
+    yd = -1003,
+    mi = -1004,
+
+    oz = -1005, //  1 oz  = 28.3495231 g
+    lb = -1006, //  1 lb  = 453.59237 g  (= 16 oz)
+    st = -1007, //  1 stone = 6350.29318 g (= 14 lb)
+
     // Undefined
     _,
 
@@ -48,24 +60,31 @@ pub const UnitScale = enum(isize) {
         var buf: [16]u8 = undefined;
         return switch (self) {
             inline .none => "",
-            inline .P, .T, .G, .M, .k, .h, .da, .d, .c, .m, .u, .n, .p, .f, .min, .hour, .year => @tagName(self),
+            inline .P, .T, .G, .M, .k, .h, .da, .d, .c, .m, .u, .n, .p, .f, .min, .hour, .year, .inch, .ft, .yd, .mi, .oz, .lb, .st => @tagName(self),
             else => std.fmt.bufPrint(&buf, "[{d}]", .{@intFromEnum(self)}) catch "[]", // This cannot be inline because of non exhaustive enum, but that's ok, it is just str, not calculation
         };
     }
 
-    /// Helper to get the actual scaling factor
     pub inline fn getFactor(self: @This()) comptime_float {
         return comptime switch (self) {
+            // Standard SI Exponents
             inline .P, .T, .G, .M, .k, .h, .da, .none, .d, .c, .m, .u, .n, .p, .f => std.math.pow(f64, 10.0, @floatFromInt(@intFromEnum(self))),
-            inline else => @floatFromInt(@intFromEnum(self)),
-        };
-    }
 
-    /// Helper to get the actual scaling factor in i32
-    pub fn getFactorInt(self: @This()) comptime_int {
-        return comptime switch (self) {
-            inline .P, .T, .G, .M, .k, .h, .da, .none, .d, .c, .m, .u, .n, .p, .f => std.math.powi(i32, 10.0, @intFromEnum(self)) catch 0,
-            inline else => @intFromEnum(self),
+            // Time Factors
+            inline .min, .hour, .year => @floatFromInt(@intFromEnum(self)),
+
+            // Imperial Length (metres)
+            inline .inch => 0.0254,
+            inline .ft => 0.3048,
+            inline .yd => 0.9144,
+            inline .mi => 1609.344,
+
+            // Imperial Mass (grams — base unit for M is gram, i.e. .none = 1 g)
+            inline .oz => 28.3495231,
+            inline .lb => 453.59237,
+            inline .st => 6350.29318,
+
+            inline else => @floatFromInt(@intFromEnum(self)),
         };
     }
 };