[git commit] tls: add a patch with optimization which _should_ give better code

[Denys Vlasenko]

commit: https://git.busybox.net/busybox/commit/?id=d728a30c211c2df6adccd64c6e2fc23387b341f2
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

...but does not.

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 networking/tls_sp_c32.patch | 142 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 142 insertions(+)

diff --git a/networking/tls_sp_c32.patch b/networking/tls_sp_c32.patch
new file mode 100644
index 000000000..7559586c9
--- /dev/null
+++ b/networking/tls_sp_c32.patch
@@ -0,0 +1,142 @@
+Somehow, gcc 6+ does this optimization same or better than the below
+hand-written optimized code (gcc seem to eliminate a32[] array, uses 32-bit
+registers/memory for "lower halves" of a32[i] elements).
+
+But there can be arches where gcc won't be this good?
+
+diff --git a/networking/tls_sp_c32.c b/networking/tls_sp_c32.c
+index 72a3be537..e8a011ad1 100644
+--- a/networking/tls_sp_c32.c
++++ b/networking/tls_sp_c32.c
+@@ -228,51 +228,96 @@ static void sp_256_rshift1_10(sp_digit* r, sp_digit* a)
+ static void sp_256_mod_mul_norm_10(sp_digit* r, const sp_digit* a)
+ {
+ 	int64_t t[8];
+-	int64_t a32[8];
++	uint32_t a32;
+ 	int64_t o;
+ 
+-	a32[0] = a[0];
+-	a32[0] |= a[1] << 26;
+-	a32[0] &= 0xffffffff;
+-	a32[1] = (sp_digit)(a[1] >> 6);
+-	a32[1] |= a[2] << 20;
+-	a32[1] &= 0xffffffff;
+-	a32[2] = (sp_digit)(a[2] >> 12);
+-	a32[2] |= a[3] << 14;
+-	a32[2] &= 0xffffffff;
+-	a32[3] = (sp_digit)(a[3] >> 18);
+-	a32[3] |= a[4] << 8;
+-	a32[3] &= 0xffffffff;
+-	a32[4] = (sp_digit)(a[4] >> 24);
+-	a32[4] |= a[5] << 2;
+-	a32[4] |= a[6] << 28;
+-	a32[4] &= 0xffffffff;
+-	a32[5] = (sp_digit)(a[6] >> 4);
+-	a32[5] |= a[7] << 22;
+-	a32[5] &= 0xffffffff;
+-	a32[6] = (sp_digit)(a[7] >> 10);
+-	a32[6] |= a[8] << 16;
+-	a32[6] &= 0xffffffff;
+-	a32[7] = (sp_digit)(a[8] >> 16);
+-	a32[7] |= a[9] << 10;
+-	a32[7] &= 0xffffffff;
+-
+ 	/*  1  1  0 -1 -1 -1 -1  0 */
+-	t[0] = 0 + a32[0] + a32[1] - a32[3] - a32[4] - a32[5] - a32[6];
+ 	/*  0  1  1  0 -1 -1 -1 -1 */
+-	t[1] = 0 + a32[1] + a32[2] - a32[4] - a32[5] - a32[6] - a32[7];
+ 	/*  0  0  1  1  0 -1 -1 -1 */
+-	t[2] = 0 + a32[2] + a32[3] - a32[5] - a32[6] - a32[7];
+ 	/* -1 -1  0  2  2  1  0 -1 */
+-	t[3] = 0 - a32[0] - a32[1] + 2 * a32[3] + 2 * a32[4] + a32[5] - a32[7];
+ 	/*  0 -1 -1  0  2  2  1  0 */
+-	t[4] = 0 - a32[1] - a32[2] + 2 * a32[4] + 2 * a32[5] + a32[6];
+ 	/*  0  0 -1 -1  0  2  2  1 */
+-	t[5] = 0 - a32[2] - a32[3] + 2 * a32[5] + 2 * a32[6] + a32[7];
+ 	/* -1 -1  0  0  0  1  3  2 */
+-	t[6] = 0 - a32[0] - a32[1] + a32[5] + 3 * a32[6] + 2 * a32[7];
+ 	/*  1  0 -1 -1 -1 -1  0  3 */
+-	t[7] = 0 + a32[0] - a32[2] - a32[3] - a32[4] - a32[5] + 3 * a32[7];
++	//t[0] = 0 + a32[0] + a32[1]            - a32[3]   - a32[4]   - a32[5]   - a32[6]             ;
++	//t[1] = 0          + a32[1] + a32[2]              - a32[4]   - a32[5]   - a32[6]   - a32[7]  ;
++	//t[2] = 0                   + a32[2]   + a32[3]              - a32[5]   - a32[6]   - a32[7]  ;
++	//t[3] = 0 - a32[0] - a32[1]            + 2*a32[3] + 2*a32[4] + a32[5]              - a32[7]  ;
++	//t[4] = 0          - a32[1] - a32[2]              + 2*a32[4] + 2*a32[5] + a32[6]             ;
++	//t[5] = 0                   - a32[2]   - a32[3]              + 2*a32[5] + 2*a32[6] + a32[7]  ;
++	//t[6] = 0 - a32[0] - a32[1]                                  + a32[5]   + 3*a32[6] + 2*a32[7];
++	//t[7] = 0 + a32[0]          - a32[2]   - a32[3]   - a32[4]   - a32[5]              + 3*a32[7];
++
++#define A32 (int64_t)a32
++	a32 = a[0];
++	a32 |= a[1] << 26;
++	t[0] = 0 + A32;
++	t[3] = 0 - A32;
++	t[6] = 0 - A32;
++	t[7] = 0 + A32;
++
++	a32 = (sp_digit)(a[1] >> 6);
++	a32 |= a[2] << 20;
++	t[0] += A32    ;
++	t[1]  = 0 + A32;
++	t[3] -= A32    ;
++	t[4]  = 0 - A32;
++	t[6] -= A32    ;
++
++	a32 = (sp_digit)(a[2] >> 12);
++	a32 |= a[3] << 14;
++	t[1] += A32    ;
++	t[2]  = 0 + A32;
++	t[4] -= A32    ;
++	t[5]  = 0 - A32;
++	t[7] -= A32    ;
++
++	a32 = (sp_digit)(a[3] >> 18);
++	a32 |= a[4] << 8;
++	t[0] -= A32  ;
++	t[2] += A32  ;
++	t[3] += 2*A32;
++	t[5] -= A32  ;
++	t[7] -= A32  ;
++
++	a32 = (sp_digit)(a[4] >> 24);
++	a32 |= a[5] << 2;
++	a32 |= a[6] << 28;
++	t[0] -= A32  ;
++	t[1] -= A32  ;
++	t[3] += 2*A32;
++	t[4] += 2*A32;
++	t[7] -= A32  ;
++
++	a32 = (sp_digit)(a[6] >> 4);
++	a32 |= a[7] << 22;
++	t[0] -= A32  ;
++	t[1] -= A32  ;
++	t[2] -= A32  ;
++	t[3] += A32  ;
++	t[4] += 2*A32;
++	t[5] += 2*A32;
++	t[6] += A32  ;
++	t[7] -= A32  ;
++
++	a32 = (sp_digit)(a[7] >> 10);
++	a32 |= a[8] << 16;
++	t[0] -= A32  ;
++	t[1] -= A32  ;
++	t[2] -= A32  ;
++	t[4] += A32  ;
++	t[5] += 2*A32;
++	t[6] += 3*A32;
++
++	a32 = (sp_digit)(a[8] >> 16);
++	a32 |= a[9] << 10;
++	t[1] -= A32  ;
++	t[2] -= A32  ;
++	t[3] -= A32  ;
++	t[5] += A32  ;
++	t[6] += 2*A32;
++	t[7] += 3*A32;
++#undef A32
+ 
+ 	t[1] += t[0] >> 32; t[0] &= 0xffffffff;
+ 	t[2] += t[1] >> 32; t[1] &= 0xffffffff;