LibF7: Tweak IEEE double multiplication.

libgcc/config/avr/libf7/
	* libf7-asm.sx (mul_mant) [AVR_HAVE_MUL]: Tweak code.

1 files changed, 107 insertions, 101 deletions

diff --git a/libgcc/config/avr/libf7/libf7-asm.sx b/libgcc/config/avr/libf7/libf7-asm.sx
index 4505764..01d1fa3 100644
--- a/libgcc/config/avr/libf7/libf7-asm.sx
+++ b/libgcc/config/avr/libf7/libf7-asm.sx
@@ -877,10 +877,14 @@ ENDF ashldi3
 ;; R18.0 = 1: No rounding.
 
 DEFUN mul_mant
+    ;; 10 = Y, R17...R10
     do_prologue_saves 10
+    ;; T = R18.0: Skip rounding?
     bst     r18,    0
+    ;; Save result address for later.
     push    r25
     push    r24
+    ;; Load A's mantissa.
     movw    ZL,     r22
     LDD     A0,     Z+0+Off
     LDD     A1,     Z+1+Off
@@ -913,26 +917,15 @@ DEFUN mul_mant
     adc     C6, ZERO
     ;; Done B6
 
-    ;; 3 * 3 -> 0:a
-    ;; 4 * 4 -> 2:1
-    ;; 5 * 5 -> 4:3
-    ldd     BB, Z+3+Off $   mul     A3, BB      $   movw    TT0, r0
-    ldd     BB, Z+4+Off $   mul     A4, BB      $   movw    TT2, r0
-    ldd     BB, Z+5+Off $   mul     A5, BB
-
-    ADD     CA, TT0     $   adc     C0, TT1
-    adc     C1, TT2     $   adc     C2, TT3
-    adc     C3, r0      $   adc     C4, r1
-    brcc .+2
-    adiw    C5, 1
-
     ;; 6 * 5 -> 5:4
     ;; 4 * 5 -> 3:2
     ;; 2 * 5 -> 1:0
     ;; 0 * 5 -> a:-
+    ldd     BB, Z+5+Off
     mul     A0, BB
-    ;; A0 done
+    ;; Done A0
 #define Atmp A0
+#define Null A0
 
     mov     Atmp, r1
     mul     A6, BB      $   movw    TT2, r0
@@ -942,82 +935,127 @@ DEFUN mul_mant
     ADD     CA, Atmp
     adc     C0, r0      $   adc     C1, r1
     adc     C2, TT0     $   adc     C3, TT1
-    adc     C4, TT2     $   adc     C5, TT3     $   clr ZERO
-    adc     C6, ZERO
+    adc     C4, TT2     $   adc     C5, TT3     $   clr Null
+    adc     C6, Null
 
     ;; 1 * 5 -> 0:a
     ;; 3 * 5 -> 2:1
-    ;; 6 * 4 -> 4:3
+    ;; 5 * 5 -> 4:3
     mul     A1, BB      $   movw    TT0, r0
     mul     A3, BB      $   movw    TT2, r0
+    mul     A5, BB
+
+    ADD     CA, TT0     $   adc     C0, TT1
+    adc     C1, TT2     $   adc     C2, TT3
+    adc     C3, r0      $   adc     C4, r1
+    adc     C5, Null    $   adc     C6, Null
+    ;; Done B5
+
+    ;; 2 * 4 -> 0:a
+    ;; 4 * 4 -> 2:1
+    ;; 6 * 4 -> 4:3
     ldd     BB, Z+4+Off
+    mul     A2, BB      $   movw    TT0, r0
+    mul     A4, BB      $   movw    TT2, r0
     mul     A6, BB
 
     ADD     CA, TT0     $   adc     C0, TT1
     adc     C1, TT2     $   adc     C2, TT3
-    adc     C3, r0      $   adc     C4, r1      $   clr ZERO
-    adc     C5, ZERO    $   adc     C6, ZERO
-    ;; B5 done
+    adc     C3, r0      $   adc     C4, r1
+    adc     C5, Null    $   adc     C6, Null
 
+    ;; 1 * 4 -> a:-
+    ;; 3 * 4 -> 1:0
+    ;; 5 * 4 -> 3:2
+    mul     A1, BB      $   mov     TT1, r1
+    mul     A3, BB      $   movw    TT2, r0
+    mul     A5, BB
+    ;; Done A1
+    ;; Done B4
+    ADD     CA, TT1
+    adc     C0, TT2     $   adc     C1, TT3
+    adc     C2, r0      $   adc     C3, r1
+    ;; Accumulate carry for C3 in TT1.
+    ;; Accumulate carry for C4 in A1.
+#define Cry3 TT1
+#define Cry4 A1
+    clr     Cry3
+    clr     Cry4
+    rol     Cry4
+
+    ;; 6 * 2 -> 2:1
     ;; 6 * 3 -> 3:2
-    ;; 6 * 1 -> 1:0
-    ;; 4 * 1 -> a:-
-    mov     TT0, A6     $   ldd TMP,  Z+3+Off
-    mov     BB,  A4     $   ldd Atmp, Z+1+Off
-    rcall   .Lmul.help.3
+    ;; 5 * 3 -> 2:1
+    ldd     BB, Z+2+Off
+    mul     A6, BB
+    add     C1, r0
+    adc     C2, r1
+    adc     Cry3, Null
 
-    ;; 5 * 4 -> 3:2
-    ;; 5 * 2 -> 1:0
-    ;; 3 * 2 -> a:-
-    mov     TT0, A5     $   ldd TMP,  Z+4+Off
-    mov     BB,  A3     $   ldd Atmp, Z+2+Off
-    rcall   .Lmul.help.3
+    ldd     BB, Z+3+Off
+    mul     A6, BB
+    add     C2, r0
+    adc     C3, r1
+    adc     Cry4, Null
+
+    mul     A5, BB
+    add     C1, r0
+    adc     C2, r1
+    adc     Cry3, Null
 
-    ;; 4 *   -> 3:2 (=0)
+    ;; Perform the remaining 11 multiplications in 4 loopings:
     ;; 4 * 3 -> 1:0
+    ;; 3 * 3 -> 0:a
     ;; 2 * 3 -> a:-
-    mov     TT0, A4     $   clr TMP
-    mov     BB,  A2     $   ldd Atmp, Z+3+Off
-    rcall   .Lmul.help.3
-
-    ;; 3 * . -> 3:2 (=0)
-    ;; 3 * 4 -> 1:0
-    ;; 1 * 4 -> a:-
-    mov     TT0, A3     $   clr TMP
-    mov     BB,  A1     $   ldd Atmp, Z+4+Off
-    rcall   .Lmul.help.3
-
-    ;; . * ? -> 3:2 (=0)
-    ;; . * 0 -> 1:0 (=0)
+    ;;
+    ;; 5 * 2 -> 1:0
+    ;; 4 * 2 -> 0:a
+    ;; 3 * 2 -> a:-
+    ;;
+    ;; 6 * 1 -> 1:0
+    ;; 5 * 1 -> 0:a
+    ;; 4 * 1 -> a:-
+    ;;
+    ;; . * 0 -> 1:0  (=0)
+    ;; 6 * 0 -> 0:a
     ;; 5 * 0 -> a:-
-    clr     TT0
-    mov     BB,  A5     $   ldd Atmp, Z+0+Off
-    rcall   .Lmul.help.3
 
-    clr TT3  ;; Asserted by .Lmul.help.2
-    ;; 6 * 2 -> 2:1
-    ;; 6 * 0 -> 0:a
-                        $   ldd TMP,  Z+2+Off
-    mov     BB, A6     ;$   ldd Atmp, Z+0+Off
-    rcall   .Lmul.help.2
+    ;; BB already contains B3, hence let Z point one past B2 so that
+    ;; the  LD *, -Z  below will pick up B2, B1, B0.
+    adiw    r30,    1 + Off+2
 
-    ;; 5 * 3 -> 2:1
-    ;; 5 * 1 -> 0:a
-                        $   ldd TMP,  Z+3+Off
-    mov     BB, A5      $   ldd Atmp, Z+1+Off
-    rcall   .Lmul.help.2
+    ;; Accumulate carry for C2 in TT2.
+#define Cry2 TT2
+    clr     Cry2
 
-    ;; 4 * . -> 2:1 (=0)
-    ;; 4 * 2 -> 0:a
-                        $   clr TMP
-    mov     BB, A4      $   ldd Atmp, Z+2+Off
-    rcall   .Lmul.help.2
+    ;; TT3 is the loop counter, iterate over B3...B0.
+    ldi     TT3,    4
+    rjmp .Loop_start
 
-    ;; 2 * . -> 2:1 (=0)
-    ;; 2 * 4 -> 0:a
-                        $   clr TMP
-    mov     BB, A2      $   ldd Atmp, Z+4+Off
-    rcall   .Lmul.help.2
+.Loop:
+    ;; We use A2...A4 below; so shift bytes of A into place.
+    mov     A2, A3
+    mov     A3, A4
+    mov     A4, A5
+    mov     A5, A6
+    clr     A6
+    ld      BB, -Z
+.Loop_start:
+    mul     A3, BB
+    ADD     CA, r0      $  adc  C0, r1  $  adc  C1, Null    $  adc  Cry2, Null
+    MUL     A2, BB
+    mov     TT0, r1
+    MUL     A4, BB
+    ADD     CA, TT0     $  adc  C0, r0  $  adc  C1, r1      $  adc  Cry2, Null
+    dec     TT3
+    brne .Loop
+
+    clr     ZERO
+    ADD     C2, Cry2
+    adc     C3, Cry3
+    adc     C4, Cry4
+    adc     C5, ZERO
+    adc     C6, ZERO
 
     ;; Finally...
 
@@ -1032,38 +1070,6 @@ DEFUN mul_mant
 
     do_epilogue_restores 10
 
-;; TT0 * Tmp  -> 3:2
-;; TT0 * Atmp -> 1:0
-;; BB  * Atmp -> a:-
-;;
-;; Clobbers : TMP, TT0...TT3.
-;; Sets     : ZERO = 0.
-.Lmul.help.3:
-    mul     TT0, TMP    $   movw    TT2, r0
-    mul     TT0, Atmp   $   movw    TT0, r0
-    mul     BB,  Atmp
-
-    ADD     CA, r1
-    adc     C0, TT0     $   adc     C1, TT1
-    adc     C2, TT2
-.Lmul.help.3.C3:        $   adc     C3, TT3     $ clr ZERO
-    adc     C4, ZERO    $   adc     C5, ZERO
-    adc     C6, ZERO
-    ret
-
-;; BB * TMP  -> 2:1
-;; BB * Atmp -> 0:a
-;;
-;; Asserts  : TT3 = 0
-;; Clobbers : TMP, TT0, TT1.
-;; Sets     : ZERO = 0.
-.Lmul.help.2:
-    mul     BB, TMP     $   movw    TT0, r0
-    mul     BB, Atmp
-    ADD     CA, r0      $   adc     C0, r1
-    adc     C1, TT0     $   adc     C2, TT1
-    rjmp .Lmul.help.3.C3
-
 ENDF mul_mant
 #endif /* F7MOD_mul_mant_ && MUL */