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Simplify vli_mmod_fast.

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Ken MacKay
2014-03-09 11:34:45 -07:00
parent ef7ca6f9e1
commit ca620d4b4a
1 changed files with 16 additions and 35 deletions
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ecc.c
+16 -35
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@@ -3658,6 +3658,7 @@ __attribute__ ((noinline))
static void vli_mmod_fast(uint8_t *RESTRICT p_result, uint8_t *RESTRICT p_product)
{
#if (ECC_ASM == ecc_asm_avr)
uint8_t l_carry = 0;
__asm__ volatile (
"in r30, __SP_L__ \n\t"
"in r31, __SP_H__ \n\t"
@@ -3668,8 +3669,6 @@ static void vli_mmod_fast(uint8_t *RESTRICT p_result, uint8_t *RESTRICT p_produc
"out __SREG__, r0 \n\t"
"out __SP_L__, r30 \n\t"
"eor r20, r20 \n\t" /* r20 = 0 (carry count) */
"adiw r30, 25 \n\t" /* we are shifting by 31 bits, so shift over 4 bytes (+ 1 since z initially points below the stack) */
"adiw r26, 40 \n\t" /* end of p_product */
"ld r18, -x \n\t" /* Load word. */
@@ -3734,7 +3733,7 @@ static void vli_mmod_fast(uint8_t *RESTRICT p_result, uint8_t *RESTRICT p_produc
"ld r19, x+ \n\t"
"adc r18, r19 \n\t"
"st y+, r18 \n\t")
"adc r20, __zero_reg__ \n\t" /* Store carry bit (carry flag is cleared). */
"adc %[carry], __zero_reg__ \n\t" /* Store carry bit (carry flag is cleared). */
/* at this point x is at the end of p_product, y is at the end of p_result, z is 20 bytes into tmp */
"sbiw r28, 20 \n\t" /* move y back to point at p_result */
@@ -3823,51 +3822,33 @@ static void vli_mmod_fast(uint8_t *RESTRICT p_result, uint8_t *RESTRICT p_produc
"adc r18, __zero_reg__ \n\t"
"st y+, r18 \n\t")
"adc r20, __zero_reg__ \n\t" /* Store carry bit (carry flag is cleared). */
"adc %[carry], __zero_reg__ \n\t" /* Store carry bit (carry flag is cleared). */
"sbiw r28, 20 \n\t" /* move y back to point at p_result */
"mmod_after_remult: \n\t"
"sbiw r30, 24 \n\t" /* move z back to point at tmp */
/* carry is <= 2, so subtract up to 2 times */
"cpse r20, __zero_reg__ \n\t"
"rcall mmod_sub \n\t"
"cpse r20, __zero_reg__ \n\t"
"rcall mmod_sub \n\t"
"rjmp mmod_end \n\t"
"mmod_sub: \n\t"
/* subtract curve_p (loaded into x) from p_result (in y) */
"ldi r26, lo8(curve_p) \n\t" /* make x point at curve_p */
"ldi r27, hi8(curve_p) \n\t"
"ld r18, y \n\t"
"ld r19, x+ \n\t"
"sub r18, r19 \n\t"
"st y+, r18 \n\t"
REPEAT(19, "ld r18, y \n\t"
"ld r19, x+ \n\t"
"sbc r18, r19 \n\t"
"st y+, r18 \n\t")
"sbiw r28, 20 \n\t" /* make y point at p_result again */
"dec r20 \n\t" /* subtract 1 from carry flag */
"ret \n\t"
"mmod_end: \n\t"
"adiw r30, 23 \n\t"
"sbiw r30, 1 \n\t" /* fix stack pointer */
"in r0, __SREG__ \n\t"
"cli \n\t"
"out __SP_H__, r31 \n\t"
"out __SREG__, r0 \n\t"
"out __SP_L__, r30 \n\t"
: "+y" (p_result), "+x" (p_product)
: "+y" (p_result), "+x" (p_product), [carry] "+r" (l_carry)
:
: "r0", "r18", "r19", "r20", "r30", "r31", "cc", "memory"
: "r0", "r18", "r19", "r30", "r31", "cc", "memory"
);
if(l_carry > 0)
{
--l_carry;
vli_sub(p_result, p_result, curve_p);
}
if(l_carry > 0)
{
vli_sub(p_result, p_result, curve_p);
}
if(vli_cmp(p_result, curve_p) > 0)
{
vli_sub(p_result, p_result, curve_p);