tls: optimize sp_256_mul_8 in P256

function                                             old     new   delta
sp_256_mont_mul_8                                    151     150      -1

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 82 insertions, 2 deletions

diff --git a/networking/tls_sp_c32.c b/networking/tls_sp_c32.c
index b99951890..e1c4cdd54 100644
--- a/networking/tls_sp_c32.c
+++ b/networking/tls_sp_c32.c
@@ -294,6 +294,85 @@ static int sp_256_sub_8(sp_digit* r, const sp_digit* a, const sp_digit* b)
 /* Multiply a and b into r. (r = a * b) */
 static void sp_256_mul_8(sp_digit* r, const sp_digit* a, const sp_digit* b)
 {
+#if ALLOW_ASM && defined(__GNUC__) && defined(__i386__)
+        sp_digit rr[15]; /* in case r coincides with a or b */
+        int k;
+        uint32_t accl;
+        uint32_t acch;
+
+        acch = accl = 0;
+        for (k = 0; k < 15; k++) {
+                int i, j;
+                uint32_t acc_hi;
+                i = k - 7;
+                if (i < 0)
+                        i = 0;
+                j = k - i;
+                acc_hi = 0;
+                do {
+////////////////////////
+//                      uint64_t m = ((uint64_t)a[i]) * b[j];
+//                      acc_hi:acch:accl += m;
+                        asm volatile (
+                        // a[i] is already loaded in %%eax
+"\n                     mull    %7"
+"\n                     addl    %%eax, %0"
+"\n                     adcl    %%edx, %1"
+"\n                     adcl    $0, %2"
+                        : "=rm" (accl), "=rm" (acch), "=rm" (acc_hi)
+                        : "0" (accl), "1" (acch), "2" (acc_hi), "a" (a[i]), "m" (b[j])
+                        : "cc", "dx"
+                        );
+////////////////////////
+                        j--;
+                        i++;
+                } while (i != 8 && i <= k);
+                rr[k] = accl;
+                accl = acch;
+                acch = acc_hi;
+        }
+        r[15] = accl;
+        memcpy(r, rr, sizeof(rr));
+#elif 0
+        //TODO: arm assembly (untested)
+        sp_digit tmp[16];
+
+        asm volatile (
+"\n             mov     r5, #0"
+"\n             mov     r6, #0"
+"\n             mov     r7, #0"
+"\n             mov     r8, #0"
+"\n     1:"
+"\n             subs    r3, r5, #28"
+"\n             movcc   r3, #0"
+"\n             sub     r4, r5, r3"
+"\n             2:"
+"\n             ldr     r14, [%[a], r3]"
+"\n             ldr     r12, [%[b], r4]"
+"\n             umull   r9, r10, r14, r12"
+"\n             adds    r6, r6, r9"
+"\n             adcs    r7, r7, r10"
+"\n             adc     r8, r8, #0"
+"\n             add     r3, r3, #4"
+"\n             sub     r4, r4, #4"
+"\n             cmp     r3, #32"
+"\n             beq     3f"
+"\n             cmp     r3, r5"
+"\n             ble     2b"
+"\n     3:"
+"\n             str     r6, [%[r], r5]"
+"\n             mov     r6, r7"
+"\n             mov     r7, r8"
+"\n             mov     r8, #0"
+"\n             add     r5, r5, #4"
+"\n             cmp     r5, #56"
+"\n             ble     1b"
+"\n             str     r6, [%[r], r5]"
+                : [r] "r" (tmp), [a] "r" (a), [b] "r" (b)
+                : "memory", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r14", "r12"
+        );
+        memcpy(r, tmp, sizeof(tmp));
+#else
         sp_digit rr[15]; /* in case r coincides with a or b */
         int i, j, k;
         uint64_t acc;
@@ -306,19 +385,20 @@ static void sp_256_mul_8(sp_digit* r, const sp_digit* a, const sp_digit* b)
                         i = 0;
                 j = k - i;
                 acc_hi = 0;
-                while (i != 8 && i <= k) {
+                do {
                         uint64_t m = ((uint64_t)a[i]) * b[j];
                         acc += m;
                         if (acc < m)
                                 acc_hi++;
                         j--;
                         i++;
-                }
+                } while (i != 8 && i <= k);
                 rr[k] = acc;
                 acc = (acc >> 32) | ((uint64_t)acc_hi << 32);
         }
         r[15] = acc;
         memcpy(r, rr, sizeof(rr));
+#endif
 }
 
 /* Shift number right one bit. Bottom bit is lost. */