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even faster cmp implementation

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This commit is contained in:
araq
2026-03-09 15:49:28 +01:00
parent 2ceb7006f7
commit e933ae6a72
1 changed files with 22 additions and 5 deletions
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27
lib/system/strs_v3.nim
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@@ -40,6 +40,8 @@ type
more: ptr LongString
proc bswap64(x: uint): uint {.importc: "__builtin_bswap64", nodecl, noSideEffect.}
proc ctz32(x: uint32): int32 {.importc: "__builtin_ctz", nodecl, noSideEffect.}
proc ctz64(x: uint64): int32 {.importc: "__builtin_ctzll", nodecl, noSideEffect.}
proc swarKey(x: uint): uint {.inline.} =
## Returns a value where inline char[0] is in the most significant byte,
@@ -63,6 +65,25 @@ template ssLenOf(bytes: uint): int =
else:
int(bytes shr (8 * (sizeof(uint) - 1)))
proc cmpShortInline(abytes, bbytes: uint; aslen, bslen: int): int {.inline.} =
let minLen = min(aslen, bslen)
if minLen > 0:
when system.cpuEndian == littleEndian:
let diffMask = (1'u shl (minLen * 8)) - 1'u
let diff = ((abytes xor bbytes) shr 8) and diffMask
if diff != 0:
let byteShift = ((when sizeof(uint) <= 4: ctz32(uint32(diff)) else: ctz64(uint64(diff))).int shr 3) * 8 + 8
let ac = (abytes shr byteShift) and 0xFF'u
let bc = (bbytes shr byteShift) and 0xFF'u
if ac < bc: return -1
return 1
else:
let aw = swarKey(abytes)
let bw = swarKey(bbytes)
if aw < bw: return -1
if aw > bw: return 1
aslen - bslen
template ssLen(s: SmallString): int =
## Load slen via a direct byte access. A byte load (movzx) lets the C compiler
## prove that slen is at offset 0, distinct from inline char writes at offsets 1+,
@@ -215,11 +236,7 @@ proc cmp(a, b: SmallString): int {.inline.} =
let aslen = ssLenOf(abytes)
let bslen = ssLenOf(bbytes)
if aslen <= AlwaysAvail and bslen <= AlwaysAvail:
let aw = swarKey(abytes)
let bw = swarKey(bbytes)
if aw < bw: return -1
if aw > bw: return 1
return aslen - bslen
return cmpShortInline(abytes, bbytes, aslen, bslen)
cmpStringPtrs(unsafeAddr a, unsafeAddr b)
proc `==`(a, b: SmallString): bool {.inline.} =