First Commit

externals/libressl/crypto/bn/arch/amd64/bignum_cmul.S

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+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+// ----------------------------------------------------------------------------
+// Multiply by a single word, z := c * y
+// Inputs c, y[n]; outputs function return (carry-out) and z[k]
+//
+//    extern uint64_t bignum_cmul
+//     (uint64_t k, uint64_t *z, uint64_t c, uint64_t n, uint64_t *y);
+//
+// Does the "z := c * y" operation where y is n digits, result z is p.
+// Truncates the result in general unless p >= n + 1.
+//
+// The return value is a high/carry word that is meaningful when p >= n as
+// giving the high part of the result. Since this is always zero if p > n,
+// it is mainly of interest in the special case p = n, i.e. where the source
+// and destination have the same nominal size, when it gives the extra word
+// of the full result.
+//
+// Standard x86-64 ABI: RDI = k, RSI = z, RDX = c, RCX = n, R8 = y, returns RAX
+// Microsoft x64 ABI:   RCX = k, RDX = z, R8 = c, R9 = n, [RSP+40] = y, returns RAX
+// ----------------------------------------------------------------------------
+
+#include "s2n_bignum_internal.h"
+
+        .intel_syntax noprefix
+        S2N_BN_SYM_VISIBILITY_DIRECTIVE(bignum_cmul)
+        S2N_BN_SYM_PRIVACY_DIRECTIVE(bignum_cmul)
+        .text
+
+#define p rdi
+#define z rsi
+#define c r9
+#define n rcx
+#define x r8
+
+#define i r10
+#define h r11
+
+
+
+S2N_BN_SYMBOL(bignum_cmul):
+	endbr64
+
+#if WINDOWS_ABI
+        push    rdi
+        push    rsi
+        mov     rdi, rcx
+        mov     rsi, rdx
+        mov     rdx, r8
+        mov     rcx, r9
+        mov     r8, [rsp+56]
+#endif
+
+// First clamp the input size n := min(p,n) since we can never need to read
+// past the p'th term of the input to generate p-digit output. Now we can
+// assume that n <= p
+
+        cmp     p, n
+        cmovc   n, p
+
+// Initialize current input/output pointer offset i and high part h.
+// But then if n = 0 skip the multiplication and go to the tail part
+
+        xor     h, h
+        xor     i, i
+        test    n, n
+        jz      tail
+
+// Move c into a safer register as multiplies overwrite rdx
+
+        mov     c, rdx
+
+// Initialization of the loop: [h,l] = c * x_0
+
+        mov     rax, [x]
+        mul     c
+        mov     [z], rax
+        mov     h, rdx
+        inc     i
+        cmp     i, n
+        jz      tail
+
+// Main loop doing the multiplications
+
+loop:
+        mov     rax, [x+8*i]
+        mul     c
+        add     rax, h
+        adc     rdx, 0
+        mov     [z+8*i], rax
+        mov     h, rdx
+        inc     i
+        cmp     i, n
+        jc      loop
+
+// Add a tail when the destination is longer
+
+tail:
+        cmp     i, p
+        jnc     end
+        mov     [z+8*i], h
+        xor     h, h
+        inc     i
+        cmp     i, p
+        jnc     end
+
+tloop:
+        mov     [z+8*i], h
+        inc     i
+        cmp     i, p
+        jc      tloop
+
+// Return the high/carry word
+
+end:
+        mov     rax, h
+
+#if WINDOWS_ABI
+        pop    rsi
+        pop    rdi
+#endif
+        ret
+
+#if defined(__linux__) && defined(__ELF__)
+.section .note.GNU-stack,"",%progbits
+#endif