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Merge pull request #5180 from Parashurama/optimize_byteswapping

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optimize byte-swapping in endians.nim
This commit is contained in:
Andreas Rumpf 2017-01-06 10:53:56 +01:00 • committed by GitHub
commit fb14ec9aae
1 changed files with 79 additions and 30 deletions
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61
lib/pure/endians.nim
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@ -10,7 +10,57 @@
## This module contains helpers that deal with different byte orders
## (`endian`:idx:).
proc swapEndian64*(outp, inp: pointer) =
when defined(gcc) or defined(llvm_gcc) or defined(clang):
const useBuiltinSwap = true
proc builtin_bswap16(a: uint16): uint16 {.
importc: "__builtin_bswap16", nodecl, nosideeffect.}
proc builtin_bswap32(a: uint32): uint32 {.
importc: "__builtin_bswap32", nodecl, nosideeffect.}
proc builtin_bswap64(a: uint64): uint64 {.
importc: "__builtin_bswap64", nodecl, nosideeffect.}
elif defined(icc):
const useBuiltinSwap = true
proc builtin_bswap16(a: uint16): uint16 {.
importc: "_bswap16", nodecl, nosideeffect.}
proc builtin_bswap32(a: uint32): uint32 {.
importc: "_bswap", nodecl, nosideeffect.}
proc builtin_bswap64(a: uint64): uint64 {.
importc: "_bswap64", nodecl, nosideeffect.}
elif defined(vcc):
const useBuiltinSwap = true
proc builtin_bswap16(a: uint16): uint16 {.
importc: "_byteswap_ushort", nodecl, header: "<intrin.h>", nosideeffect.}
proc builtin_bswap32(a: uint32): uint32 {.
importc: "_byteswap_ulong", nodecl, header: "<intrin.h>", nosideeffect.}
proc builtin_bswap64(a: uint64): uint64 {.
importc: "_byteswap_uint64", nodecl, header: "<intrin.h>", nosideeffect.}
else:
const useBuiltinSwap = false
when useBuiltinSwap:
proc swapEndian64*(outp, inp: pointer) {.inline, nosideeffect.}=
var i = cast[ptr uint64](inp)
var o = cast[ptr uint64](outp)
o[] = builtin_bswap64(i[])
proc swapEndian32*(outp, inp: pointer) {.inline, nosideeffect.}=
var i = cast[ptr uint32](inp)
var o = cast[ptr uint32](outp)
o[] = builtin_bswap32(i[])
proc swapEndian16*(outp, inp: pointer) {.inline, nosideeffect.}=
var i = cast[ptr uint16](inp)
var o = cast[ptr uint16](outp)
o[] = builtin_bswap16(i[])
else:
proc swapEndian64*(outp, inp: pointer) =
## copies `inp` to `outp` swapping bytes. Both buffers are supposed to
## contain at least 8 bytes.
var i = cast[cstring](inp)
@ -24,7 +74,7 @@ proc swapEndian64*(outp, inp: pointer) =
o[6] = i[1]
o[7] = i[0]
proc swapEndian32*(outp, inp: pointer) =
proc swapEndian32*(outp, inp: pointer) =
## copies `inp` to `outp` swapping bytes. Both buffers are supposed to
## contain at least 4 bytes.
var i = cast[cstring](inp)
@ -34,12 +84,11 @@ proc swapEndian32*(outp, inp: pointer) =
o[2] = i[1]
o[3] = i[0]
proc swapEndian16*(outp, inp: pointer) =
proc swapEndian16*(outp, inp: pointer) =
## copies `inp` to `outp` swapping bytes. Both buffers are supposed to
## contain at least 2 bytes.
var
i = cast[cstring](inp)
o = cast[cstring](outp)
var i = cast[cstring](inp)
var o = cast[cstring](outp)
o[0] = i[1]
o[1] = i[0]