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Optimization: Removed unnecessary divides #306

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Optimization: Removed unnecessary divides #306

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dc6dc27
Removed unnecessary divides
Sc00bz Oct 16, 2020
bba500b
Replaced divide with reciprocal fix point multiply
Sc00bz Oct 16, 2020
05a8c29
Removed data dependent branching
Sc00bz Feb 22, 2021
28cccd1
Removed unnecessary divide
Sc00bz Feb 24, 2021
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11 changes: 6 additions & 5 deletions src/core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -200,8 +200,8 @@ uint32_t index_alpha(const argon2_instance_t *instance,
* Other lanes : (SYNC_POINTS - 1) last segments
*/
uint32_t reference_area_size;
uint64_t relative_position;
uint32_t start_position, absolute_position;
uint64_t relative_position, absolute_position;
uint32_t start_position;

if (0 == position->pass) {
/* First pass */
Expand Down Expand Up @@ -251,9 +251,10 @@ uint32_t index_alpha(const argon2_instance_t *instance,
}

/* 1.2.6. Computing absolute position */
absolute_position = (start_position + relative_position) %
instance->lane_length; /* absolute position */
return absolute_position;
absolute_position = start_position + relative_position -
instance->lane_length;
absolute_position += instance->lane_length & (absolute_position >> 32);
return (uint32_t) absolute_position;
}

/* Single-threaded version for p=1 case */
Expand Down
24 changes: 16 additions & 8 deletions src/opt.c
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Original file line number Diff line number Diff line change
Expand Up @@ -178,6 +178,8 @@ void fill_segment(const argon2_instance_t *instance,
uint64_t pseudo_rand, ref_index, ref_lane;
uint32_t prev_offset, curr_offset;
uint32_t starting_index, i;
uint32_t lanes_reciprocal = 0;
uint32_t lanes = instance->lanes;
#if defined(__AVX512F__)
__m512i state[ARGON2_512BIT_WORDS_IN_BLOCK];
#elif defined(__AVX2__)
Expand Down Expand Up @@ -222,23 +224,23 @@ void fill_segment(const argon2_instance_t *instance,
curr_offset = position.lane * instance->lane_length +
position.slice * instance->segment_length + starting_index;

if (0 == curr_offset % instance->lane_length) {
if ((0 == position.slice) && (0 == starting_index)) {
/* Last block in this lane */
prev_offset = curr_offset + instance->lane_length - 1;
} else {
/* Previous block */
prev_offset = curr_offset - 1;
}

/* Fixed point multiply constant for dividing by lanes */
if ((lanes & (lanes - 1)) != 0) {
lanes_reciprocal = (uint32_t) (UINT64_C(0x100000000) / lanes);
}

memcpy(state, ((instance->memory + prev_offset)->v), ARGON2_BLOCK_SIZE);

for (i = starting_index; i < instance->segment_length;
++i, ++curr_offset, ++prev_offset) {
/*1.1 Rotating prev_offset if needed */
if (curr_offset % instance->lane_length == 1) {
prev_offset = curr_offset - 1;
}

++i, ++curr_offset) {
/* 1.2 Computing the index of the reference block */
/* 1.2.1 Taking pseudo-random value from the previous block */
if (data_independent_addressing) {
Expand All @@ -248,10 +250,16 @@ void fill_segment(const argon2_instance_t *instance,
pseudo_rand = address_block.v[i % ARGON2_ADDRESSES_IN_BLOCK];
} else {
pseudo_rand = instance->memory[prev_offset].v[0];
prev_offset = curr_offset;
}

/* 1.2.2 Computing the lane of the reference block */
ref_lane = ((pseudo_rand >> 32)) % instance->lanes;
if (lanes_reciprocal == 0) {
ref_lane = (pseudo_rand >> 32) & (lanes - 1);
} else {
ref_lane = (pseudo_rand >> 32) - (((pseudo_rand >> 32) * lanes_reciprocal) >> 32) * lanes - lanes;
ref_lane += lanes & (ref_lane >> 32);
}

if ((position.pass == 0) && (position.slice == 0)) {
/* Can not reference other lanes yet */
Expand Down