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> Can you convert this function to Win64 and also write a pure pascal version?  
                                                                                
  procedure AlphaBlendLineMasterAndColor(Destination: Pointer; Count: Integer;  
  ConstantAlpha, Color: Integer);                                               
  // EAX contains Destination                                                   
  // EDX contains Count                                                         
  // ECX contains ConstantAlpha                                                 
  // Color is passed on the stack                                               
                                                                                
  asm                                                                           
          // The used formula is: target = (alpha * color + (256 - alpha) *     
  target) / 256.                                                                
          // alpha * color (factor 1) and 256 - alpha (factor 2) are constant   
  values which can be calculated in advance.                                    
          // The remaining calculation is therefore: target = (F1 + F2 *        
  target) / 256                                                                 
                                                                                
          // Load MM3 with the constant alpha value (replicate it for every     
  component).                                                                   
          // Expand it to word size. (Every calculation here works on word      
  sized operands.)                                                              
          DB      $0F, $6E, $D9          /// MOVD      MM3, ECX                 
          DB      $0F, $61, $DB          /// PUNPCKLWD MM3, MM3                 
          DB      $0F, $62, $DB          /// PUNPCKLDQ MM3, MM3                 
                                                                                
          // Calculate factor 2.                                                
          MOV     ECX, $100                                                     
          DB      $0F, $6E, $D1          /// MOVD      MM2, ECX                 
          DB      $0F, $61, $D2          /// PUNPCKLWD MM2, MM2                 
          DB      $0F, $62, $D2          /// PUNPCKLDQ MM2, MM2                 
          DB      $0F, $F9, $D3          /// PSUBW     MM2, MM3             //  
  MM2 contains now: 255 - alpha = F2                                            
                                                                                
          // Now calculate factor 1. Alpha is still in MM3, but the r and b     
  components of Color must be swapped.                                          
          MOV     ECX, [Color]                                                  
          BSWAP   ECX                                                           
          ROR     ECX, 8                                                        
          DB      $0F, $6E, $C9          /// MOVD      MM1, ECX             //  
  Load the color and convert to word sized values.                              
          DB      $0F, $EF, $E4          /// PXOR      MM4, MM4                 
          DB      $0F, $60, $CC          /// PUNPCKLBW MM1, MM4                 
          DB      $0F, $D5, $CB          /// PMULLW    MM1, MM3             //  
  MM1 contains now: color * alpha = F1                                          
                                                                                
  @1:     // The pixel loop calculates an entire pixel in one run.              
          DB      $0F, $6E, $00          /// MOVD      MM0, [EAX]               
          DB      $0F, $60, $C4          /// PUNPCKLBW MM0, MM4                 
                                                                                
          DB      $0F, $D5, $C2          /// PMULLW    MM0, MM2             //  
  calculate F1 + F2 * target                                                    
          DB      $0F, $FD, $C1          /// PADDW     MM0, MM1                 
          DB      $0F, $71, $D0, $08     /// PSRLW     MM0, 8               //  
  divide by 256                                                                 
                                                                                
          DB      $0F, $67, $C0          /// PACKUSWB  MM0, MM0             //  
  convert words to bytes with saturation                                        
          DB      $0F, $7E, $00          /// MOVD      [EAX], MM0           //  
  store the result                                                              
                                                                                
          ADD     EAX, 4                                                        
          DEC     EDX                                                           
          JNZ     @1                                                            
  end;                                                                          
                                                                                

● Here's a Win64 port (using XMM lower-half so we don't need EMMS) and a clean
  pure-pascal fallback. I kept the formula and pixel layout identical to the
  original (input Color is a Delphi TColor-style 0x00BBGGRR, destination is
  32-bpp BGRA).

  procedure AlphaBlendLineMasterAndColor(Destination: pointer; Count: integer;
    ConstantAlpha, Color: integer);
  {$IFDEF PUREPASCAL}
  type
    TPixel = packed record
      B, G, R, A: byte;
    end;
    PPixel = ^TPixel;
  var
    pixel   : PPixel;
    alpha   : integer;
    invAlpha: integer;
    f1B     : integer;
    f1G     : integer;
    f1R     : integer;
  begin
    // The used formula is: target = (alpha * color + (256 - alpha) * target) / 
  256.
    alpha    := ConstantAlpha and $FF;
    invAlpha := 256 - alpha;

    // Color is 0x00BBGGRR; pre-multiply each component with alpha (= F1).
    f1B := ((Color shr 16) and $FF) * alpha;
    f1G := ((Color shr  8) and $FF) * alpha;
    f1R := ( Color         and $FF) * alpha;

    pixel := PPixel(Destination);
    for var i := 0 to Count - 1 do begin
      pixel^.B := (pixel^.B * invAlpha + f1B) shr 8;
      pixel^.G := (pixel^.G * invAlpha + f1G) shr 8;
      pixel^.R := (pixel^.R * invAlpha + f1R) shr 8;
      pixel^.A := (pixel^.A * invAlpha)       shr 8;
      Inc(pixel);
    end;
  end;
  {$ELSE}{$IFDEF CPUX64}
  // RCX = Destination, EDX = Count, R8D = ConstantAlpha, R9D = Color
  asm
          // Load alpha into XMM3 (replicated as 4 words in the low qword).
          MOVD      XMM3, R8D
          PUNPCKLWD XMM3, XMM3
          PUNPCKLDQ XMM3, XMM3

          // Calculate factor 2: F2 = 256 - alpha.
          MOV       R10D, $100
          MOVD      XMM2, R10D
          PUNPCKLWD XMM2, XMM2
          PUNPCKLDQ XMM2, XMM2
          PSUBW     XMM2, XMM3

          // Now calculate factor 1. Alpha is still in XMM3, but the r and b
          // components of Color must be swapped.
          MOV       R10D, R9D
          BSWAP     R10D
          ROR       R10D, 8
          MOVD      XMM1, R10D                 // load the color and convert to 
  word sized values
          PXOR      XMM4, XMM4
          PUNPCKLBW XMM1, XMM4
          PMULLW    XMM1, XMM3                 // XMM1 = color * alpha = F1

  @1:     // The pixel loop calculates an entire pixel in one run.
          MOVD      XMM0, dword ptr [RCX]
          PUNPCKLBW XMM0, XMM4

          PMULLW    XMM0, XMM2                 // F2 * target
          PADDW     XMM0, XMM1                 // + F1
          PSRLW     XMM0, 8                    // divide by 256

          PACKUSWB  XMM0, XMM0                 // words -> bytes with saturation
          MOVD      dword ptr [RCX], XMM0      // store the result

          ADD       RCX, 4
          DEC       EDX
          JNZ       @1
  end;
  {$ELSE}
  // (original Win32 asm goes here)
  asm
          DB      $0F, $6E, $D9          /// MOVD      MM3, ECX
          // ... etc.
  end;
  {$ENDIF}{$ENDIF}

  Notes on the conversions:

  - Win64 calling convention: Destination→RCX, Count→EDX, ConstantAlpha→R8D,
  Color→R9D. R10D is used as scratch instead of ECX (RCX now holds the pointer).
  - MMX → XMM: The instructions used (MOVD, PUNPCKL*, PSUBW, PXOR, PMULLW,
  PADDW, PSRLW, PACKUSWB) all behave identically on the low 64 bits of XMM.
  Using XMM avoids the FPU/MMX state aliasing and the trailing EMMS you'd
  otherwise need on x64.
  - Mnemonics: Modern Delphi's x64 assembler accepts SSE2 mnemonics directly, so
   the DB byte-encoding workaround from the original is no longer required.
  - Pure pascal version: The math stays bounded (max 255*256 + 0 = 65280, >>8 = 
  255), so no explicit saturation is needed — the implicit byte truncation never
   loses high bits for valid inputs. The alpha channel is attenuated by
  (256-alpha)/256, matching what the assembly does (the high word of F1 is zero
  because the BSWAP+ROR puts $00 into byte 3).
  - Caveat preserved from the original: when Count = 0 the assembly loops
  underflow (DEC/JNZ never hits zero); the pure-pascal for loop handles Count = 
  0 correctly. If you want bit-exact behavior, add an early if Count <= 0 then 
  Exit at the top of the asm versions.

✻ Brewed for 3m 0s

> Please verify that all three versions are functionally identical.             

● I traced through all three with concrete inputs. Within the implicit input
  contract (ConstantAlpha ∈ [0,255], Color is TColor 0x00BBGGRR, Count > 0),
  they produce identical results — but I found two edge-case discrepancies you
  should know about.

  Trace summary

  For each pixel byte the formula reduces to (with a = alpha, ia = 256‑a):

  ┌─────────┬────────────────────────┬────────────────────────┬────────────┐
  │ Channel │       Win32 asm        │       Win64 asm        │   Pure     │
  │         │                        │                        │   pascal   │
  ├─────────┼────────────────────────┼────────────────────────┼────────────┤
  │         │                        │                        │ (B·ia +    │
  │ B       │ (B·ia + BB·a) ÷ 256    │ (B·ia + BB·a) ÷ 256    │ f1B) shr 8 │
  │         │                        │                        │  ✓         │
  ├─────────┼────────────────────────┼────────────────────────┼────────────┤
  │         │                        │                        │ (G·ia +    │
  │ G       │ (G·ia + GG·a) ÷ 256    │ (G·ia + GG·a) ÷ 256    │ f1G) shr 8 │
  │         │                        │                        │  ✓         │
  ├─────────┼────────────────────────┼────────────────────────┼────────────┤
  │         │                        │                        │ (R·ia +    │
  │ R       │ (R·ia + RR·a) ÷ 256    │ (R·ia + RR·a) ÷ 256    │ f1R) shr 8 │
  │         │                        │                        │  ✓         │
  ├─────────┼────────────────────────┼────────────────────────┼────────────┤
  │         │ (A·ia +                │ (A·ia +                │ (A·ia) shr │
  │ A       │ HighByte(Color)·a) ÷   │ HighByte(Color)·a) ÷   │  8 ⚠       │
  │         │ 256                    │ 256                    │            │
  └─────────┴────────────────────────┴────────────────────────┴────────────┘

  The XMM port matches MMX exactly because every instruction used (MOVD,
  PUNPCKL{BW,WD,DQ}, PSUBW, PXOR, PMULLW, PADDW, PSRLW, PACKUSWB) has identical
  word-lane semantics on the low 64 bits of XMM as on MMX, and MOVD r32→XMM/MMX
  zero-extends the upper bits in both.

  Numeric range check (proves no overflow / saturation difference)

  For B, BB ∈ [0,255], a ∈ [0,255]:
  - B·ia + BB·a = 256·B + a·(BB−B), max = 255·256 = 65280 → fits in word, so
  PADDW doesn't wrap.
  - After >> 8, max = 255 → PACKUSWB saturation never fires; pure-pascal byte
  truncation loses nothing.
  - f1B + B·ia in pure pascal stays in integer range, no overflow.

  Discrepancies I found

  1. High byte of Color (real difference). The asm versions do BSWAP/ROR then
  PUNPCKLBW against zero, which lifts byte[3] of the swapped color into word[3]
  of F1, so it gets blended into the alpha channel. The pure-pascal version
  drops it. For TColor inputs the high byte is $00 and the result is the same,
  but if anyone ever passes a 32-bpp ARGB value, the alpha channel will diverge.

  Fix in the pure-pascal version:

    f1B := ((Color shr 16) and $FF) * alpha;
    f1G := ((Color shr  8) and $FF) * alpha;
    f1R := ( Color         and $FF) * alpha;
    f1A := ((Color shr 24) and $FF) * alpha;   // <-- add
    ...
      pixel^.A := (pixel^.A * invAlpha + f1A) shr 8;   // <-- add f1A

  2. Count = 0 (latent bug carried over). Both asm versions do DEC EDX; JNZ @1,
  so passing Count = 0 underflows to $FFFFFFFF and runs ~4 billion iterations
  off the end of the buffer. The pure-pascal for var i := 0 to Count - 1 handles
   it correctly. If you want the asm versions to share that safety, add a guard:

          TEST    EDX, EDX
          JZ      @done
  @1:     ...
          JNZ     @1
  @done:

  3. ConstantAlpha outside [0,255] (theoretical only). Asm uses the low 16 bits
  of the register (PUNPCKLWD takes word[0]); pure pascal masks to 8 bits (and 
  $FF). For values 256..65535 they would diverge, and PMULLW would also start
  truncating. Not a real concern given the documented contract, but worth
  knowing if anyone passes garbage.

  Conclusion

  With the f1A addition, the three versions are bit-identical for the entire
  valid input range, including 32-bpp ARGB colors. Without it, they agree on all
   TColor-style inputs (high byte = 0) and disagree only on the alpha channel
  for ARGB inputs. The Count = 0 divergence is pre-existing in the original
  Win32 code; the pure-pascal version is the one that's safer, not the other way
   around.

✻ Baked for 2m 41s

> Please fix all the bugs and output the final result.                          

● procedure AlphaBlendLineMasterAndColor(Destination: pointer; Count: integer;
    ConstantAlpha, Color: integer);
  {$IFDEF PUREPASCAL}
  type
    TPixel = packed record
      B, G, R, A: byte;
    end;
    PPixel = ^TPixel;
  var
    pixel   : PPixel;
    alpha   : integer;
    invAlpha: integer;
    f1B     : integer;
    f1G     : integer;
    f1R     : integer;
    f1A     : integer;
  begin
    if Count <= 0 then
      Exit;

    // The used formula is: target = (alpha * color + (256 - alpha) * target) / 
  256.
    alpha    := ConstantAlpha and $FF;
    invAlpha := 256 - alpha;

    // Pre-multiply each component of Color with alpha (= F1). The high byte is
    // included so 32-bpp ARGB inputs blend the alpha channel the same way the
    // asm versions do; for TColor inputs (high byte = 0) it has no effect.
    f1B := ((Color shr 16) and $FF) * alpha;
    f1G := ((Color shr  8) and $FF) * alpha;
    f1R := ( Color         and $FF) * alpha;
    f1A := ((Color shr 24) and $FF) * alpha;

    pixel := PPixel(Destination);
    for var i := 0 to Count - 1 do begin
      pixel^.B := (pixel^.B * invAlpha + f1B) shr 8;
      pixel^.G := (pixel^.G * invAlpha + f1G) shr 8;
      pixel^.R := (pixel^.R * invAlpha + f1R) shr 8;
      pixel^.A := (pixel^.A * invAlpha + f1A) shr 8;
      Inc(pixel);
    end;
  end;
  {$ELSE}{$IFDEF CPUX64}
  // RCX = Destination, EDX = Count, R8D = ConstantAlpha, R9D = Color
  asm
          // Guard against Count = 0 (DEC/JNZ would otherwise underflow).
          TEST      EDX, EDX
          JZ        @done

          // Load alpha into XMM3 (replicated as 4 words in the low qword).
          MOVD      XMM3, R8D
          PUNPCKLWD XMM3, XMM3
          PUNPCKLDQ XMM3, XMM3

          // Calculate factor 2: F2 = 256 - alpha.
          MOV       R10D, $100
          MOVD      XMM2, R10D
          PUNPCKLWD XMM2, XMM2
          PUNPCKLDQ XMM2, XMM2
          PSUBW     XMM2, XMM3

          // Now calculate factor 1. Alpha is still in XMM3, but the r and b
          // components of Color must be swapped.
          MOV       R10D, R9D
          BSWAP     R10D
          ROR       R10D, 8
          MOVD      XMM1, R10D
          PXOR      XMM4, XMM4
          PUNPCKLBW XMM1, XMM4
          PMULLW    XMM1, XMM3                 // XMM1 = color * alpha = F1

  @1:     // The pixel loop calculates an entire pixel in one run.
          MOVD      XMM0, dword ptr [RCX]
          PUNPCKLBW XMM0, XMM4

          PMULLW    XMM0, XMM2                 // F2 * target
          PADDW     XMM0, XMM1                 // + F1
          PSRLW     XMM0, 8                    // divide by 256

          PACKUSWB  XMM0, XMM0                 // words -> bytes with saturation
          MOVD      dword ptr [RCX], XMM0      // store the result

          ADD       RCX, 4
          DEC       EDX
          JNZ       @1
  @done:
  end;
  {$ELSE}
  // EAX = Destination, EDX = Count, ECX = ConstantAlpha, Color on the stack.
  asm
          // The used formula is: target = (alpha * color + (256 - alpha) * 
  target) / 256.
          // Guard against Count = 0 (DEC/JNZ would otherwise underflow).
          TEST    EDX, EDX
          JZ      @done

          // Load MM3 with the constant alpha value (replicated for every 
  component).
          DB      $0F, $6E, $D9          /// MOVD      MM3, ECX
          DB      $0F, $61, $DB          /// PUNPCKLWD MM3, MM3
          DB      $0F, $62, $DB          /// PUNPCKLDQ MM3, MM3

          // Calculate factor 2.
          MOV     ECX, $100
          DB      $0F, $6E, $D1          /// MOVD      MM2, ECX
          DB      $0F, $61, $D2          /// PUNPCKLWD MM2, MM2
          DB      $0F, $62, $D2          /// PUNPCKLDQ MM2, MM2
          DB      $0F, $F9, $D3          /// PSUBW     MM2, MM3             // 
  MM2 = 256 - alpha = F2

          // Now calculate factor 1. The r and b components of Color must be 
  swapped.
          MOV     ECX, [Color]
          BSWAP   ECX
          ROR     ECX, 8
          DB      $0F, $6E, $C9          /// MOVD      MM1, ECX
          DB      $0F, $EF, $E4          /// PXOR      MM4, MM4
          DB      $0F, $60, $CC          /// PUNPCKLBW MM1, MM4
          DB      $0F, $D5, $CB          /// PMULLW    MM1, MM3             // 
  MM1 = color * alpha = F1

  @1:     // The pixel loop calculates an entire pixel in one run.
          DB      $0F, $6E, $00          /// MOVD      MM0, [EAX]
          DB      $0F, $60, $C4          /// PUNPCKLBW MM0, MM4

          DB      $0F, $D5, $C2          /// PMULLW    MM0, MM2             // 
  F2 * target
          DB      $0F, $FD, $C1          /// PADDW     MM0, MM1             // +
   F1
          DB      $0F, $71, $D0, $08     /// PSRLW     MM0, 8               // 
  divide by 256

          DB      $0F, $67, $C0          /// PACKUSWB  MM0, MM0             // 
  words -> bytes with saturation
          DB      $0F, $7E, $00          /// MOVD      [EAX], MM0           // 
  store the result

          ADD     EAX, 4
          DEC     EDX
          JNZ     @1
  @done:
  end;
  {$ENDIF}{$ENDIF}

  Changes from the previous version:

  - Pure pascal: added f1A := ((Color shr 24) and $FF) * alpha and folded it
  into the pixel^.A assignment, so 32-bpp ARGB inputs match the asm versions
  byte-for-byte. Also added an early if Count <= 0 then Exit (already implicit
  in the for, but explicit makes the contract obvious).
  - Win64 asm: TEST EDX, EDX / JZ @done guard at the top, @done: label after the
   loop.
  - Win32 asm: same guard; the original DB-encoded MMX block is otherwise
  unchanged.

  All three now produce identical output for any Count >= 0, any Color (TColor
  or 32-bpp ARGB), and any ConstantAlpha in [0, 255].

✻ Sautéed for 1m 10s