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Improve ARM asm a bit (particularly for Thumb devices)
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@kmackay
kmackay committed Jan 10, 2016
1 parent 39bedb1 commit 7db3158
Showing 1 changed file with 36 additions and 42 deletions.
78 changes: 36 additions & 42 deletions asm_arm.inc
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Original file line number Diff line number Diff line change
Expand Up @@ -996,17 +996,16 @@ uECC_VLI_API void uECC_vli_mult(uECC_word_t *result,
"muls %[r5], %[r0], %[r5] \n\t" /* r5 = a0 * b1 */
"muls %[r0], %[r4], %[r0] \n\t" /* r0 = a0 * b0 */

"movs %[r4], #0 \n\t" /* r4 = 0 */
"adds %[r3], %[r5] \n\t" /* r3 = b0 * a1 + a0 * b1 */
"adcs %[r4], %[r4] \n\t" /* r4 = carry */
"lsls %[r4], #16 \n\t" /* r4 = carry << 16 */
"adds %[r6], %[r4] \n\t" /* r6 = a1 * b1 + carry */
/* Add middle terms */
"lsls %[r4], %[r3], #16 \n\t"
"lsrs %[r3], %[r3], #16 \n\t"
"adds %[r0], %[r4] \n\t"
"adcs %[r6], %[r3] \n\t"

"lsls %[r4], %[r3], #16 \n\t" /* r4 = (b0 * a1 + a0 * b1) << 16 */
"lsrs %[r3], #16 \n\t" /* r3 = (b0 * a1 + a0 * b1) >> 16 */
"adds %[r0], %[r4] \n\t" /* r0 = low word = a0 * b0 + ((b0 * a1 + a0 * b1) << 16) */
"adcs %[r6], %[r3] \n\t" /* r6 = high word =
a1 * b1 + carry + ((b0 * a1 + a0 * b1) >> 16) */
"lsls %[r4], %[r5], #16 \n\t"
"lsrs %[r5], %[r5], #16 \n\t"
"adds %[r0], %[r4] \n\t"
"adcs %[r6], %[r5] \n\t"

"pop {%[r3]} \n\t" /* r3 = c0 */
"pop {%[r4]} \n\t" /* r4 = c1 */
Expand Down Expand Up @@ -1087,13 +1086,11 @@ uECC_VLI_API void uECC_vli_square(uECC_word_t *result,

"cmp %[i], %[tt] \n\t" /* (i < k - i) ? */
"bge 4f \n\t" /* if i >= k - i, skip */
"lsls %[t1], #1 \n\t" /* high word << 1 */
"adc %[c2], %[c2], #0 \n\t" /* add carry bit to c2 */
"lsls %[t0], #1 \n\t" /* low word << 1 */
"adc %[t1], %[t1], #0 \n\t" /* add carry bit to high word */
"adds %[c0], %[c0], %[t0] \n\t" /* add low word to c0 */
"adcs %[c1], %[c1], %[t1] \n\t" /* add high word to c1, including carry */
"adcs %[c2], %[c2], #0 \n\t" /* add carry to c2 */

"4: \n\t"

"adds %[c0], %[c0], %[t0] \n\t" /* add low word to c0 */
"adcs %[c1], %[c1], %[t1] \n\t" /* add high word to c1, including carry */
"adcs %[c2], %[c2], #0 \n\t" /* add carry to c2 */
Expand Down Expand Up @@ -1137,6 +1134,7 @@ uECC_VLI_API void uECC_vli_square(uECC_word_t *result,
"lsls %[r2], #1 \n\t" /* r2 = (num_words - 1) * 8 */
"mov r9, %[r2] \n\t" /* r9 = (num_words - 1) * 8 */
"movs %[r2], #0 \n\t" /* c0 = 0 */
"mov r10, %[r2] \n\t" /* r10 = 0 */
"movs %[r3], #0 \n\t" /* c1 = 0 */
"movs %[r4], #0 \n\t" /* c2 = 0 */
"movs %[r5], #0 \n\t" /* k = 0 */
Expand All @@ -1157,7 +1155,7 @@ uECC_VLI_API void uECC_vli_square(uECC_word_t *result,
"push {%[r4]} \n\t"
"push {%[r3]} \n\t"
"push {%[r2]} \n\t" /* push things, r2 (c0) is at the top of stack. */
"subs %[r7], %[r5], %[r6] \n\t" /* r7 = k - i */
"subs %[r7], %[r5], %[r6] \n\t" /* r7 = k - i */

"ldr %[r3], [%[r1], %[r7]] \n\t" /* r3 = left[k - i] */
"ldr %[r0], [%[r1], %[r6]] \n\t" /* r0 = left[i] */
Expand All @@ -1174,36 +1172,32 @@ uECC_VLI_API void uECC_vli_square(uECC_word_t *result,
"muls %[r4], %[r0], %[r4] \n\t" /* r4 = a0 * b1 */
"muls %[r0], %[r3], %[r0] \n\t" /* r0 = a0 * b0 */

"movs %[r3], #0 \n\t" /* r3 = 0 */
"adds %[r2], %[r4] \n\t" /* r2 = b0 * a1 + a0 * b1 */
"adcs %[r3], %[r3] \n\t" /* r3 = carry */
"lsls %[r3], #16 \n\t" /* r3 = carry << 16 */
"adds %[r5], %[r3] \n\t" /* r5 = a1 * b1 + carry */
/* Add middle terms */
"lsls %[r3], %[r2], #16 \n\t"
"lsrs %[r2], %[r2], #16 \n\t"
"adds %[r0], %[r3] \n\t"
"adcs %[r5], %[r2] \n\t"

"lsls %[r3], %[r2], #16 \n\t" /* r3 = (b0 * a1 + a0 * b1) << 16 */
"lsrs %[r2], #16 \n\t" /* r2 = (b0 * a1 + a0 * b1) >> 16 */
"adds %[r0], %[r3] \n\t" /* r0 = low word = a0 * b0 + ((b0 * a1 + a0 * b1) << 16) */
"adcs %[r5], %[r2] \n\t" /* r5 = high word =
a1 * b1 + carry + ((b0 * a1 + a0 * b1) >> 16) */

"movs %[r3], #0 \n\t" /* r3 = 0 */
"cmp %[r6], %[r7] \n\t" /* (i < k - i) ? */
"mov %[r7], %[r3] \n\t" /* r7 = 0 (does not affect condition) */
"bge 4f \n\t" /* if i >= k - i, skip */
"lsls %[r5], #1 \n\t" /* high word << 1 */
"adcs %[r7], %[r3] \n\t" /* r7 = carry bit for c2 */
"lsls %[r0], #1 \n\t" /* low word << 1 */
"adcs %[r5], %[r3] \n\t" /* add carry from shift to high word */
"lsls %[r3], %[r4], #16 \n\t"
"lsrs %[r4], %[r4], #16 \n\t"
"adds %[r0], %[r3] \n\t"
"adcs %[r5], %[r4] \n\t"

"4: \n\t"
/* Add to acc, doubling if necessary */
"pop {%[r2]} \n\t" /* r2 = c0 */
"pop {%[r3]} \n\t" /* r3 = c1 */
"pop {%[r4]} \n\t" /* r4 = c2 */
"adds %[r2], %[r0] \n\t" /* add low word to c0 */
"adcs %[r3], %[r5] \n\t" /* add high word to c1, including carry */
"movs %[r0], #0 \n\t" /* r0 = 0 (does not affect carry bit) */
"adcs %[r4], %[r0] \n\t" /* add carry to c2 */
"adds %[r4], %[r7] \n\t" /* add carry from doubling (if any) */

"cmp %[r6], %[r7] \n\t" /* (i < k - i) ? */
"mov %[r7], r10 \n\t" /* r7 = 0 (does not affect flags) */
"bge 4f \n\t" /* if i >= k - i, skip */
"adds %[r2], %[r0] \n\t" /* add low word to c0 */
"adcs %[r3], %[r5] \n\t" /* add high word to c1, including carry */
"adcs %[r4], %[r7] \n\t" /* add carry to c2 */
"4: \n\t"
"adds %[r2], %[r0] \n\t" /* add low word to c0 */
"adcs %[r3], %[r5] \n\t" /* add high word to c1, including carry */
"adcs %[r4], %[r7] \n\t" /* add carry to c2 */

"pop {%[r5]} \n\t" /* r5 = k */

Expand Down Expand Up @@ -1236,7 +1230,7 @@ uECC_VLI_API void uECC_vli_square(uECC_word_t *result,
: [r2] "+l" (num_words), [r3] "=&l" (r3), [r4] "=&l" (r4),
[r5] "=&l" (r5), [r6] "=&l" (r6), [r7] "=&l" (r7)
: [r0] "l" (result), [r1] "l" (left)
: "r8", "r9", "cc", "memory"
: "r8", "r9", "r10", "cc", "memory"
);
#endif
}
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