micro optimization, removing bounds checks and allowing caching in CP…

…U register for the costs array.

Fastenshtein_1_0_0_8.asm

@@ -0,0 +1,106 @@
+; Fastenshtein.Benchmarking.FastenshteinOld.Fastenshtein_1_0_0_8.DistanceFrom(System.String)
+       push      r15
+       push      r14
+       push      rdi
+       push      rsi
+       push      rbp
+       push      rbx
+       sub       rsp,28
+       mov       rax,[rcx+10]
+       cmp       dword ptr [rax+8],0 -- costs.Length == 0
+       je        near ptr RETURN_VALUE_LENGTH
+       xor       r8d,r8d
+       cmp       dword ptr [rax+8],0
+       jle       short OUTTER_LOOP_INTRO
+ARRAY_POPULATE:
+       lea       r10d,[r8+1]
+       mov       r9,rax
+       mov       r11d,[r9+8]
+       cmp       r8d,r11d
+       jae       near ptr OUT_OF_RANGE
+       mov       r11d,r8d
+       mov       [r9+r11*4+10],r10d
+       cmp       [rax+8],r10d
+       mov       r8d,r10d
+       jg        short ARRAY_POPULATE
+OUTTER_LOOP_INTRO:
+       xor       r8d,r8d
+       mov       r10d,[rdx+8]
+       test      r10d,r10d
+       jle       near ptr RETURN
+       mov       rcx,[rcx+8]
+OUTTER_LOOP:
+       mov       r9d,r8d
+       mov       r11d,r9d
+       mov       ebx,r9d
+       movzx     ebx,word ptr [rdx+rbx*2+0C]
+       xor       esi,esi
+       cmp       dword ptr [rcx+8],0
+       jle       short OUTTER_LOOP_END
+INNER_LOOP:
+       mov       rdi,rax
+       mov       ebp,[rdi+8]
+       cmp       esi,ebp
+       jae       near ptr OUT_OF_RANGE
+       mov       r14d,esi
+       mov       edi,[rdi+r14*4+10]
+       mov       r15,rcx
+       cmp       esi,[r15+8]
+       jae       short OUT_OF_RANGE
+       movzx     r15d,word ptr [r15+r14*2+0C]
+       cmp       r15d,ebx
+       je        short M01_L06
+       cmp       r11d,r9d
+       jge       short M01_L04
+       mov       r9d,r11d
+M01_L04:
+       cmp       edi,r9d
+       jge       short M01_L05
+       mov       r9d,edi
+M01_L05:
+       inc       r9d
+M01_L06:
+       mov       r11,rax
+       cmp       esi,ebp
+       jae       short OUT_OF_RANGE
+       mov       [r11+r14*4+10],r9d
+       mov       r11d,r9d
+       inc       esi
+       cmp       [rcx+8],esi
+       mov       r9d,edi
+       jg        short INNER_LOOP
+OUTTER_LOOP_END:
+       inc       r8d
+       cmp       r10d,r8d
+       jg        short OUTTER_LOOP
+RETURN:
+       mov       rdx,rax
+       mov       eax,[rax+8]
+       dec       eax
+       mov       ebp,[rdx+8]
+       cmp       eax,ebp
+       jae       short OUT_OF_RANGE
+       mov       eax,[rdx+rax*4+10]
+       add       rsp,28
+       pop       rbx
+       pop       rbp
+       pop       rsi
+       pop       rdi
+       pop       r14
+       pop       r15
+       ret
+RETURN_VALUE_LENGTH:
+       mov       r10d,[rdx+8]
+       mov       eax,r10d
+       add       rsp,28
+       pop       rbx
+       pop       rbp
+       pop       rsi
+       pop       rdi
+       pop       r14
+       pop       r15
+       ret
+OUT_OF_RANGE:
+       call      CORINFO_HELP_RNGCHKFAIL
+       int       3
+; Total bytes of code 266

Fastenshtein_cost_cpy.asm

@@ -0,0 +1,95 @@
+; Fastenshtein.Levenshtein.DistanceFrom(System.String)
+       push      r15
+       push      r14
+       push      rdi
+       push      rsi
+       push      rbp
+       push      rbx
+       sub       rsp,28
+       mov       rax,[rcx+10]
+       mov       r8d,[rax+8]
+       test      r8d,r8d -- costs.Length == 0
+       je        near ptr RETURN_VALUE_LENGTH
+       xor       r10d,r10d
+       test      r8d,r8d
+       jle       short OUTTER_LOOP_INTRO
+ARRAY_POPULATE:
+       lea       r9d,[r10+1]
+       mov       r10d,r10d
+       mov       [rax+r10*4+10],r9d
+       cmp       r8d,r9d -- r8d is cached cost length
+       mov       r10d,r9d
+       jg        short ARRAY_POPULATE
+OUTTER_LOOP_INTRO:
+       xor       r10d,r10d
+       mov       r9d,[rdx+8]
+       test      r9d,r9d
+       jle       short RETURN
+       mov       rcx,[rcx+8]
+OUTTER_LOOP:
+       mov       r11d,r10d
+       mov       ebx,r11d
+       mov       esi,r11d
+       movzx     esi,word ptr [rdx+rsi*2+0C]
+       xor       edi,edi
+       cmp       dword ptr [rcx+8],0
+       jle       short OUTTER_LOOP_END
+       nop
+INNER_LOOP:
+       cmp       edi,r8d
+       jae       short OUT_OF_RANGE
+       mov       ebp,edi
+       mov       r14d,[rax+rbp*4+10]
+       mov       r15,rcx
+       cmp       edi,[r15+8]
+       jae       short OUT_OF_RANGE
+       movzx     r15d,word ptr [r15+rbp*2+0C]
+       cmp       r15d,esi
+       je        short M01_L06
+       cmp       ebx,r11d
+       jge       short M01_L04
+       mov       r11d,ebx
+M01_L04:
+       cmp       r14d,r11d
+       jge       short M01_L05
+       mov       r11d,r14d
+M01_L05:
+       inc       r11d
+M01_L06:
+       mov       [rax+rbp*4+10],r11d
+       mov       ebx,r11d
+       inc       edi
+       cmp       [rcx+8],edi
+       mov       r11d,r14d
+       jg        short INNER_LOOP
+OUTTER_LOOP_END:
+       inc       r10d
+       cmp       r9d,r10d
+       jg        short OUTTER_LOOP
+RETURN:
+       dec       r8d
+       mov       edx,r8d
+       mov       eax,[rax+rdx*4+10]
+       add       rsp,28
+       pop       rbx
+       pop       rbp
+       pop       rsi
+       pop       rdi
+       pop       r14
+       pop       r15
+       ret
+RETURN_VALUE_LENGTH:
+       mov       r9d,[rdx+8]
+       mov       eax,r9d
+       add       rsp,28
+       pop       rbx
+       pop       rbp
+       pop       rsi
+       pop       rdi
+       pop       r14
+       pop       r15
+       ret
+OUT_OF_RANGE:
+       call      CORINFO_HELP_RNGCHKFAIL
+       int       3
+; Total bytes of code 222

src/Fastenshtein/Levenshtein.cs

@@ -36,15 +36,17 @@ public Levenshtein(string value)
         /// <returns>Difference. 0 complete match.</returns>
         public int DistanceFrom(string value)
         {
+            var costs = this.costs;
+
             if (costs.Length == 0)
             {
                 return value.Length;
             }
 
             // Add indexing for insertion to first row
-            for (int i = 0; i < this.costs.Length;)
+            for (int i = 0; i < costs.Length;)
             {
-                this.costs[i] = ++i;
+                costs[i] = ++i;
             }
 
             for (int i = 0; i < value.Length; i++)
@@ -87,7 +89,7 @@ public int DistanceFrom(string value)
                 }
             }
 
-            return this.costs[this.costs.Length - 1];
+            return costs[costs.Length - 1];
         }
     }
 }