Reduce number of additions for x86_64 ecc_192_modp.

diff --git a/ChangeLog b/ChangeLog
index 7d397d719254c1c90adfbe47a6255988659fef16..93643d335becf33a6c7dfac3eb218835639476e9 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2013-02-28  Niels Möller  <nisse@lysator.liu.se>
 
+       * x86_64/ecc-192-modp.asm: Reorganized to reduce number of
+       additions. Use setc instruction.
+
        * examples/Makefile.in: Let $(HOGWEED_TARGETS) depend on
        ../libhogweed.a.
 

diff --git a/x86_64/ecc-192-modp.asm b/x86_64/ecc-192-modp.asm
index 288340f9d13be58c290c76d4140d0c9a239cd823..5812070b88908f0a3c48513d25fa5af48a07d80b 100644 (file)
--- a/x86_64/ecc-192-modp.asm
+++ b/x86_64/ecc-192-modp.asm
@@ -20,50 +20,53 @@ C MA 02111-1301, USA.
        .file "ecc-192-modp.asm"
 
 define(<RP>, <%rsi>)
-define(<T1>, <%rdi>) C Overlaps unused ecc input
-define(<T2>, <%rcx>)
-define(<T3>, <%rdx>)
-define(<T4>, <%r8>)
-define(<T5>, <%r9>)
-define(<T6>, <%r10>)
+define(<T0>, <%rdi>) C Overlaps unused ecc input
+define(<T1>, <%rcx>)
+define(<T2>, <%rdx>)
+define(<T3>, <%r8>)
+define(<H>, <%r9>)
+define(<C1>, <%r10>)
+define(<C2>, <%r11>)
 
        C ecc_192_modp (const struct ecc_curve *ecc, mp_limb_t *rp)
        .text
        ALIGN(4)
 PROLOGUE(nettle_ecc_192_modp)
        W64_ENTRY(2, 0)
-       C First: (B+1)*{r5, r4} < B^3 + B^2 - B
-       mov     32(RP), T1
-       mov     40(RP), T2
-       mov     T2, T3
-       xor     T4, T4
-       add     T1, T2
-       adc     $0, T3
-       adc     $0, T4
+       mov     16(RP), T2
+       mov     24(RP), T3
+       mov     40(RP), H
+       xor     C1, C1
+       xor     C2, C2
 
-       add     8(RP), T1
-       adc     16(RP), T2
-       adc     24(RP), T3
-       adc     $0, T4
-       C Sum is < 2B^4 + B^3 - B - 1, so {T4, T3} < 3B
+       add     H, T2
+       adc     H, T3
+       C Carry to be added in at T1 and T2
+       setc    LREG(C2)
+       
+       mov     8(RP), T1
+       mov     32(RP), H
+       adc     H, T1
+       adc     H, T2
+       C Carry to be added in at T0 and T1
+       setc    LREG(C1)
+       
+       mov     (RP), T0
+       adc     T3, T0
+       adc     T3, T1
+       adc     $0, C2
 
-       C Next: (B+1) * {T4, T3} < 3B^2 + 2B
-       mov     T4, T5
-       add     T3, T4
-       adc     $0, T5
+       C Add in C1 and C2
+       add     C1, T1
+       adc     C2, T2
+       setc    LREG(C1)
 
-       xor     T6, T6
-       add     (RP), T3
-       adc     T4, T1
-       adc     T5, T2
-       adc     $0, T6
-
-       C Fold in final carry.
-       add     T6, T3
-       adc     T6, T1
+       C Fold final carry.
+       adc     $0, T0
+       adc     C1, T1
        adc     $0, T2
 
-       mov     T3, (RP)
+       mov     T0, (RP)
        mov     T1, 8(RP)
        mov     T2, 16(RP)