diff options
Diffstat (limited to 'src/liblzma/rangecoder/range_decoder.h')
| -rw-r--r-- | src/liblzma/rangecoder/range_decoder.h | 491 |
1 files changed, 491 insertions, 0 deletions
diff --git a/src/liblzma/rangecoder/range_decoder.h b/src/liblzma/rangecoder/range_decoder.h index 7f768dc2..0480e116 100644 --- a/src/liblzma/rangecoder/range_decoder.h +++ b/src/liblzma/rangecoder/range_decoder.h @@ -416,4 +416,495 @@ do { \ t_offset &= ~t_match_bit ^ rc_mask) */ + +//////////// +// x86-64 // +//////////// + +#if defined(__x86_64__) && (defined(__GNUC__) || defined(__clang__)) + +// rc_asm_y and rc_asm_n are used as arguments to macros to control which +// strings to include or omit. +#define rc_asm_y(str) str +#define rc_asm_n(str) + +// There are a few possible variations for normalization. +// This is the smallest variant which is also used by LZMA SDK. +// +// - This has partial register write (the MOV from (%[in_ptr])). +// +// - INC saves one byte in code size over ADD. False dependency on +// partial flags from INC shouldn't become a problem on any processor +// because the instructions after normalization don't read the flags +// until SUB which sets all flags. +// +#define rc_asm_normalize \ + "cmp %[top_value], %[range]\n\t" \ + "jae 1f\n\t" \ + "shl %[shift_bits], %[code]\n\t" \ + "mov (%[in_ptr]), %b[code]\n\t" \ + "shl %[shift_bits], %[range]\n\t" \ + "inc %[in_ptr]\n" \ + "1:\n" + +// rc_asm_calc(prob) is roughly equivalent to the C version of rc_if_0(prob)... +// +// rc_bound = (rc.range >> RC_BIT_MODEL_TOTAL_BITS) * (prob); +// if (rc.code < rc_bound) +// +// ...but the bound is stored in "range": +// +// t0 = range; +// range = (range >> RC_BIT_MODEL_TOTAL_BITS) * (prob); +// t0 -= range; +// t1 = code; +// code -= range; +// +// The carry flag (CF) from the last subtraction holds the negation of +// the decoded bit (if CF==0 then the decoded bit is 1). +// The values in t0 and t1 are needed for rc_update_0(prob) and +// rc_update_1(prob). If the bit is 0, rc_update_0(prob)... +// +// rc.range = rc_bound; +// +// ...has already been done but the "code -= range" has to be reverted using +// the old value stored in t1. (Also, prob needs to be updated.) +// +// If the bit is 1, rc_update_1(prob)... +// +// rc.range -= rc_bound; +// rc.code -= rc_bound; +// +// ...is already done for "code" but the value for "range" needs to be taken +// from t0. (Also, prob needs to be updated here as well.) +// +// The assignments from t0 and t1 can be done in a branchless manner with CMOV +// after the instructions from this macro. The CF from SUB tells which moves +// are needed. +#define rc_asm_calc(prob) \ + "mov %[range], %[t0]\n\t" \ + "shr %[bit_model_total_bits], %[range]\n\t" \ + "imul %[" prob "], %[range]\n\t" \ + "sub %[range], %[t0]\n\t" \ + "mov %[code], %[t1]\n\t" \ + "sub %[range], %[code]\n\t" + +// Also, prob needs to be updated: The update math depends on the decoded bit. +// It can be expressed in a few slightly different ways but this is fairly +// convenient here: +// +// prob -= (prob + (bit ? 0 : RC_BIT_MODEL_OFFSET)) >> RC_MOVE_BITS; +// +// To do it in branchless way when the negation of the decoded bit is in CF, +// both "prob" and "prob + RC_BIT_MODEL_OFFSET" are needed. Then the desired +// value can be picked with CMOV. The addition can be done using LEA without +// affecting CF. +// +// (This prob update method is a tiny bit different from LZMA SDK 23.01. +// In the LZMA SDK a single register is reserved solely for a constant to +// be used with CMOV when updating prob. That is fine since there are enough +// free registers to do so. The method used here uses one fewer register, +// which is valuable with inline assembly.) +// +// * * * +// +// In bittree decoding, each (unrolled) loop iteration decodes one bit +// and needs one prob variable. To make it faster, the prob variable of +// the iteration N+1 is loaded during iteration N. There are two possible +// prob variables to choose from for N+1. Both are loaded from memory and +// the correct one is chosen with CMOV using the same CF as is used for +// other things described above. +// +// This preloading/prefetching requires an extra register. To avoid +// useless moves from "preloaded prob register" to "current prob register", +// the macros swap between the two registers for odd and even iterations. +// +// * * * +// +// Finally, the decoded bit has to be stored in "symbol". Since the negation +// of the bit is in CF, this can be done with SBB: symbol -= CF - 1. That is, +// if the decoded bit is 0 (CF==1) the operation is a no-op "symbol -= 0" +// and when bit is 1 (CF==0) the operation is "symbol -= 0 - 1" which is +// the same as "symbol += 1". +// +// The instructions for all things are intertwined for a few reasons: +// - freeing temporary registers for new use +// - not modifying CF too early +// - instruction scheduling +// +// The first and last iterations can cheat a little. For example, +// on the first iteration "symbol" is known to start from 1 so it +// doesn't need to be read; it can even be immediately initialized +// to 2 to prepare for the second iteration of the loop. +// +// * * * +// +// a = number of the current prob variable (0 or 1) +// b = number of the next prob variable (1 or 0) +// *_only = rc_asm_y or _n to include or exclude code marked with them +#define rc_asm_bittree(a, b, first_only, middle_only, last_only) \ + first_only( \ + "movzw 2(%[probs_base]), %[prob" #a "]\n\t" \ + "mov $2, %[symbol]\n\t" \ + "movzw 4(%[probs_base]), %[prob" #b "]\n\t" \ + ) \ + middle_only( \ + /* Note the scaling of 4 instead of 2: */ \ + "movzw (%[probs_base], %q[symbol], 4), %[prob" #b "]\n\t" \ + ) \ + last_only( \ + "add %[symbol], %[symbol]\n\t" \ + ) \ + \ + rc_asm_normalize \ + rc_asm_calc("prob" #a) \ + \ + "cmovae %[t0], %[range]\n\t" \ + \ + first_only( \ + "movzw 6(%[probs_base]), %[t0]\n\t" \ + "cmovae %[t0], %[prob" #b "]\n\t" \ + ) \ + middle_only( \ + "movzw 2(%[probs_base], %q[symbol], 4), %[t0]\n\t" \ + "lea (%q[symbol], %q[symbol]), %[symbol]\n\t" \ + "cmovae %[t0], %[prob" #b "]\n\t" \ + ) \ + last_only( \ + /*"lea (%q[symbol], %q[symbol]), %[symbol]\n\t"*/ \ + ) \ + \ + "lea %c[bit_model_offset](%q[prob" #a "]), %[t0]\n\t" \ + "cmovb %[t1], %[code]\n\t" \ + "mov %[symbol], %[t1]\n\t" \ + "cmovae %[prob" #a "], %[t0]\n\t" \ + \ + first_only( \ + "sbb $-1, %[symbol]\n\t" \ + ) \ + middle_only( \ + "sbb $-1, %[symbol]\n\t" \ + ) \ + last_only( \ + "sbb %[last_sbb], %[symbol]\n\t" \ + ) \ + \ + "shr %[move_bits], %[t0]\n\t" \ + "sub %[t0], %[prob" #a "]\n\t" \ + /* Scaling of 1 instead of 2 because symbol <<= 1. */ \ + "mov %w[prob" #a "], (%[probs_base], %q[t1], 1)\n\t" + +// NOTE: The order of variables in __asm__ can affect speed and code size. +#define rc_asm_bittree_n(probs_base_var, final_add, asm_str) \ +do { \ + uint32_t t0; \ + uint32_t t1; \ + uint32_t t_prob0; \ + uint32_t t_prob1; \ + \ + __asm__( \ + asm_str \ + : \ + [range] "+&r"(rc.range), \ + [code] "+&r"(rc.code), \ + [t0] "=&r"(t0), \ + [t1] "=&r"(t1), \ + [prob0] "=&r"(t_prob0), \ + [prob1] "=&r"(t_prob1), \ + [symbol] "=&r"(symbol), \ + [in_ptr] "+&r"(rc_in_ptr) \ + : \ + [probs_base] "r"(probs_base_var), \ + [last_sbb] "n"(-1 - (final_add)), \ + [top_value] "n"(RC_TOP_VALUE), \ + [shift_bits] "n"(RC_SHIFT_BITS), \ + [bit_model_total_bits] "n"(RC_BIT_MODEL_TOTAL_BITS), \ + [bit_model_offset] "n"(RC_BIT_MODEL_OFFSET), \ + [move_bits] "n"(RC_MOVE_BITS) \ + : \ + "cc", "memory"); \ +} while (0) + +#undef rc_bittree3 +#define rc_bittree3(probs_base_var, final_add) \ + rc_asm_bittree_n(probs_base_var, final_add, \ + rc_asm_bittree(0, 1, rc_asm_y, rc_asm_n, rc_asm_n) \ + rc_asm_bittree(1, 0, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(0, 1, rc_asm_n, rc_asm_n, rc_asm_y) \ + ) + +#undef rc_bittree6 +#define rc_bittree6(probs_base_var, final_add) \ + rc_asm_bittree_n(probs_base_var, final_add, \ + rc_asm_bittree(0, 1, rc_asm_y, rc_asm_n, rc_asm_n) \ + rc_asm_bittree(1, 0, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(0, 1, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(1, 0, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(0, 1, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(1, 0, rc_asm_n, rc_asm_n, rc_asm_y) \ + ) + +#undef rc_bittree8 +#define rc_bittree8(probs_base_var, final_add) \ + rc_asm_bittree_n(probs_base_var, final_add, \ + rc_asm_bittree(0, 1, rc_asm_y, rc_asm_n, rc_asm_n) \ + rc_asm_bittree(1, 0, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(0, 1, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(1, 0, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(0, 1, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(1, 0, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(0, 1, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree(1, 0, rc_asm_n, rc_asm_n, rc_asm_y) \ + ) + + +// Fixed-sized reverse bittree +// +// This uses the indexing that constructs the final value in symbol directly. +// add = 1, 2, 4, 8 +// dcur = -, 4, 8, 16 +// dnext0 = 4, 8, 16, - +// dnext0 = 6, 12, 24, - +#define rc_asm_bittree_rev(a, b, add, dcur, dnext0, dnext1, \ + first_only, middle_only, last_only) \ + first_only( \ + "movzw 2(%[probs_base]), %[prob" #a "]\n\t" \ + "xor %[symbol], %[symbol]\n\t" \ + "movzw 4(%[probs_base]), %[prob" #b "]\n\t" \ + ) \ + middle_only( \ + "movzw " #dnext0 "(%[probs_base], %q[symbol], 2), " \ + "%[prob" #b "]\n\t" \ + ) \ + \ + rc_asm_normalize \ + rc_asm_calc("prob" #a) \ + \ + "cmovae %[t0], %[range]\n\t" \ + \ + first_only( \ + "movzw 6(%[probs_base]), %[t0]\n\t" \ + "cmovae %[t0], %[prob" #b "]\n\t" \ + ) \ + middle_only( \ + "movzw " #dnext1 "(%[probs_base], %q[symbol], 2), %[t0]\n\t" \ + "cmovae %[t0], %[prob" #b "]\n\t" \ + ) \ + \ + "lea " #add "(%q[symbol]), %[t0]\n\t" \ + "cmovb %[t1], %[code]\n\t" \ + middle_only( \ + "mov %[symbol], %[t1]\n\t" \ + ) \ + last_only( \ + "mov %[symbol], %[t1]\n\t" \ + ) \ + "cmovae %[t0], %[symbol]\n\t" \ + "lea %c[bit_model_offset](%q[prob" #a "]), %[t0]\n\t" \ + "cmovae %[prob" #a "], %[t0]\n\t" \ + \ + "shr %[move_bits], %[t0]\n\t" \ + "sub %[t0], %[prob" #a "]\n\t" \ + first_only( \ + "mov %w[prob" #a "], 2(%[probs_base])\n\t" \ + ) \ + middle_only( \ + "mov %w[prob" #a "], " \ + #dcur "(%[probs_base], %q[t1], 2)\n\t" \ + ) \ + last_only( \ + "mov %w[prob" #a "], " \ + #dcur "(%[probs_base], %q[t1], 2)\n\t" \ + ) + +#undef rc_bittree_rev4 +#define rc_bittree_rev4(probs_base_var) \ +rc_asm_bittree_n(probs_base_var, 4, \ + rc_asm_bittree_rev(0, 1, 1, -, 4, 6, rc_asm_y, rc_asm_n, rc_asm_n) \ + rc_asm_bittree_rev(1, 0, 2, 4, 8, 12, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree_rev(0, 1, 4, 8, 16, 24, rc_asm_n, rc_asm_y, rc_asm_n) \ + rc_asm_bittree_rev(1, 0, 8, 16, -, -, rc_asm_n, rc_asm_n, rc_asm_y) \ +) + + +#undef rc_bit_add_if_1 +#define rc_bit_add_if_1(probs_base_var, dest_var, value_to_add_if_1) \ +do { \ + uint32_t t0; \ + uint32_t t1; \ + uint32_t t2 = (value_to_add_if_1); \ + uint32_t t_prob; \ + uint32_t t_index; \ + \ + __asm__( \ + "movzw (%[probs_base], %q[symbol], 2), %[prob]\n\t" \ + "mov %[symbol], %[index]\n\t" \ + \ + "add %[dest], %[t2]\n\t" \ + "add %[symbol], %[symbol]\n\t" \ + \ + rc_asm_normalize \ + rc_asm_calc("prob") \ + \ + "cmovae %[t0], %[range]\n\t" \ + "lea %c[bit_model_offset](%q[prob]), %[t0]\n\t" \ + "cmovb %[t1], %[code]\n\t" \ + "cmovae %[prob], %[t0]\n\t" \ + \ + "cmovae %[t2], %[dest]\n\t" \ + "sbb $-1, %[symbol]\n\t" \ + \ + "sar %[move_bits], %[t0]\n\t" \ + "sub %[t0], %[prob]\n\t" \ + "mov %w[prob], (%[probs_base], %q[index], 2)" \ + : \ + [range] "+&r"(rc.range), \ + [code] "+&r"(rc.code), \ + [t0] "=&r"(t0), \ + [t1] "=&r"(t1), \ + [prob] "=&r"(t_prob), \ + [index] "=&r"(t_index), \ + [symbol] "+&r"(symbol), \ + [t2] "+&r"(t2), \ + [dest] "+&r"(dest_var), \ + [in_ptr] "+&r"(rc_in_ptr) \ + : \ + [probs_base] "r"(probs_base_var), \ + [top_value] "n"(RC_TOP_VALUE), \ + [shift_bits] "n"(RC_SHIFT_BITS), \ + [bit_model_total_bits] "n"(RC_BIT_MODEL_TOTAL_BITS), \ + [bit_model_offset] "n"(RC_BIT_MODEL_OFFSET), \ + [move_bits] "n"(RC_MOVE_BITS) \ + : \ + "cc", "memory"); \ +} while (0) + + +// Literal decoding uses a normal 8-bit bittree but literal with match byte +// is more complex in picking the probability variable from the correct +// subtree. This doesn't use preloading/prefetching of the next prob because +// there are four choices instead of two. +// +// FIXME? The first iteration starts with symbol = 1 so it could be optimized +// by a tiny amount. +#define rc_asm_matched_literal(nonlast_only) \ + "add %[offset], %[symbol]\n\t" \ + "and %[offset], %[match_bit]\n\t" \ + "add %[match_bit], %[symbol]\n\t" \ + \ + "movzw (%[probs_base], %q[symbol], 2), %[prob]\n\t" \ + \ + "add %[symbol], %[symbol]\n\t" \ + \ + nonlast_only( \ + "xor %[match_bit], %[offset]\n\t" \ + "add %[match_byte], %[match_byte]\n\t" \ + ) \ + \ + rc_asm_normalize \ + rc_asm_calc("prob") \ + \ + "cmovae %[t0], %[range]\n\t" \ + "lea %c[bit_model_offset](%q[prob]), %[t0]\n\t" \ + "cmovb %[t1], %[code]\n\t" \ + "mov %[symbol], %[t1]\n\t" \ + "cmovae %[prob], %[t0]\n\t" \ + \ + nonlast_only( \ + "cmovae %[match_bit], %[offset]\n\t" \ + "mov %[match_byte], %[match_bit]\n\t" \ + ) \ + \ + "sbb $-1, %[symbol]\n\t" \ + \ + "shr %[move_bits], %[t0]\n\t" \ + /* Undo symbol += match_bit + offset: */ \ + "and $0x1FF, %[symbol]\n\t" \ + "sub %[t0], %[prob]\n\t" \ + \ + /* Scaling of 1 instead of 2 because symbol <<= 1. */ \ + "mov %w[prob], (%[probs_base], %q[t1], 1)\n\t" + + +#undef rc_matched_literal +#define rc_matched_literal(probs_base_var, match_byte_value) \ +do { \ + uint32_t t0; \ + uint32_t t1; \ + uint32_t t_prob; \ + uint32_t t_match_byte = (match_byte_value) << 1; \ + uint32_t t_match_bit = t_match_byte; \ + uint32_t t_offset = 0x100; \ + symbol = 1; \ + \ + __asm__( \ + rc_asm_matched_literal(rc_asm_y) \ + rc_asm_matched_literal(rc_asm_y) \ + rc_asm_matched_literal(rc_asm_y) \ + rc_asm_matched_literal(rc_asm_y) \ + rc_asm_matched_literal(rc_asm_y) \ + rc_asm_matched_literal(rc_asm_y) \ + rc_asm_matched_literal(rc_asm_y) \ + rc_asm_matched_literal(rc_asm_n) \ + : \ + [range] "+&r"(rc.range), \ + [code] "+&r"(rc.code), \ + [t0] "=&r"(t0), \ + [t1] "=&r"(t1), \ + [prob] "=&r"(t_prob), \ + [match_bit] "+&r"(t_match_bit), \ + [symbol] "+&r"(symbol), \ + [match_byte] "+&r"(t_match_byte), \ + [offset] "+&r"(t_offset), \ + [in_ptr] "+&r"(rc_in_ptr) \ + : \ + [probs_base] "r"(probs_base_var), \ + [top_value] "n"(RC_TOP_VALUE), \ + [shift_bits] "n"(RC_SHIFT_BITS), \ + [bit_model_total_bits] "n"(RC_BIT_MODEL_TOTAL_BITS), \ + [bit_model_offset] "n"(RC_BIT_MODEL_OFFSET), \ + [move_bits] "n"(RC_MOVE_BITS) \ + : \ + "cc", "memory"); \ +} while (0) + + +// Doing the loop in asm instead of C seems to help a little. +#undef rc_direct +#define rc_direct(dest_var, count_var) \ +do { \ + uint32_t t0; \ + uint32_t t1; \ + \ + __asm__( \ + "2:\n\t" \ + "add %[dest], %[dest]\n\t" \ + "lea 1(%q[dest]), %[t1]\n\t" \ + \ + rc_asm_normalize \ + \ + "shr $1, %[range]\n\t" \ + "mov %[code], %[t0]\n\t" \ + "sub %[range], %[code]\n\t" \ + "cmovns %[t1], %[dest]\n\t" \ + "cmovs %[t0], %[code]\n\t" \ + "dec %[count]\n\t" \ + "jnz 2b\n\t" \ + : \ + [range] "+&r"(rc.range), \ + [code] "+&r"(rc.code), \ + [t0] "=&r"(t0), \ + [t1] "=&r"(t1), \ + [dest] "+&r"(dest_var), \ + [count] "+&r"(count_var), \ + [in_ptr] "+&r"(rc_in_ptr) \ + : \ + [top_value] "n"(RC_TOP_VALUE), \ + [shift_bits] "n"(RC_SHIFT_BITS) \ + : \ + "cc", "memory"); \ +} while (0) + +#endif // x86_64 + #endif |