Faster parts 1-6 and part 7 skeleton

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day1.fs

@@ -5,21 +5,13 @@ open System
 [<RequireQualifiedAccess>]
 module Day1 =
 
-    let firstDigit (s : ReadOnlySpan<char>) =
-        let mutable pos = 0
-
-        while '0' > s.[pos] || s.[pos] > '9' do
-            pos <- pos + 1
-
+    let inline firstDigit (s : ReadOnlySpan<char>) =
+        let pos = s.IndexOfAnyInRange ('0', '9')
         byte s.[pos] - byte '0'
 
     // No surrogate pairs please!
-    let lastDigit (s : ReadOnlySpan<char>) =
-        let mutable pos = s.Length - 1
-
-        while '0' > s.[pos] || s.[pos] > '9' do
-            pos <- pos - 1
-
+    let inline lastDigit (s : ReadOnlySpan<char>) =
+        let pos = s.LastIndexOfAnyInRange ('0', '9')
         byte s.[pos] - byte '0'
 
     let part1 (s : string) =
@@ -35,35 +27,66 @@ module Day1 =
 
         total
 
-    let table =
-        [|
-            "one", 1uy
-            "two", 2uy
-            "three", 3uy
-            "four", 4uy
-            "five", 5uy
-            "six", 6uy
-            "seven", 7uy
-            "eight", 8uy
-            "nine", 9uy
-        |]
+    let isDigitSpelled (s : ReadOnlySpan<char>) (pos : int) (answer : byref<byte>) =
+        // Can't be bothered to write a jump-table compiler
+        if s.[pos] >= '0' && s.[pos] <= '9' then
+            answer <- byte s.[pos] - byte '0'
+        else if s.[pos] = 'o' then
+            if pos + 2 < s.Length && s.[pos + 1] = 'n' && s.[pos + 2] = 'e' then
+                answer <- 1uy
+        elif s.[pos] = 't' then
+            if pos + 2 < s.Length && s.[pos + 1] = 'w' && s.[pos + 2] = 'o' then
+                answer <- 2uy
+            elif
+                pos + 4 < s.Length
+                && s.[pos + 1] = 'h'
+                && s.[pos + 2] = 'r'
+                && s.[pos + 3] = 'e'
+                && s.[pos + 4] = 'e'
+            then
+                answer <- 3uy
+        elif s.[pos] = 'f' then
+            if pos + 3 < s.Length then
+                if s.[pos + 1] = 'o' && s.[pos + 2] = 'u' && s.[pos + 3] = 'r' then
+                    answer <- 4uy
+                elif s.[pos + 1] = 'i' && s.[pos + 2] = 'v' && s.[pos + 3] = 'e' then
+                    answer <- 5uy
+        elif s.[pos] = 's' then
+            if pos + 2 < s.Length && s.[pos + 1] = 'i' && s.[pos + 2] = 'x' then
+                answer <- 6uy
+            elif
+                pos + 4 < s.Length
+                && s.[pos + 1] = 'e'
+                && s.[pos + 2] = 'v'
+                && s.[pos + 3] = 'e'
+                && s.[pos + 4] = 'n'
+            then
+                answer <- 7uy
+        elif s.[pos] = 'e' then
+            if
+                pos + 4 < s.Length
+                && s.[pos + 1] = 'i'
+                && s.[pos + 2] = 'g'
+                && s.[pos + 3] = 'h'
+                && s.[pos + 4] = 't'
+            then
+                answer <- 8uy
+        elif s.[pos] = 'n' then
+            if
+                pos + 3 < s.Length
+                && s.[pos + 1] = 'i'
+                && s.[pos + 2] = 'n'
+                && s.[pos + 3] = 'e'
+            then
+                answer <- 9uy
 
     let firstDigitIncSpelled (s : ReadOnlySpan<char>) =
         let mutable pos = 0
         let mutable answer = 255uy
 
         while answer = 255uy do
-            if s.[pos] >= '0' && s.[pos] <= '9' then
-                answer <- byte s.[pos] - byte '0'
-            else
-                for i, value in table do
-                    if
-                        pos + i.Length < s.Length
-                        && MemoryExtensions.SequenceEqual (s.Slice (pos, i.Length), i)
-                    then
-                        answer <- value
-
-                pos <- pos + 1
+            isDigitSpelled s pos &answer
+            pos <- pos + 1
 
         answer
 
@@ -72,17 +95,8 @@ module Day1 =
         let mutable answer = 255uy
 
         while answer = 255uy do
-            if s.[pos] >= '0' && s.[pos] <= '9' then
-                answer <- byte s.[pos] - byte '0'
-            else
-                for i, value in table do
-                    if
-                        pos - i.Length + 1 >= 0
-                        && MemoryExtensions.SequenceEqual (s.Slice (pos - i.Length + 1, i.Length), i)
-                    then
-                        answer <- value
-
-                pos <- pos - 1
+            isDigitSpelled s pos &answer
+            pos <- pos - 1
 
         answer