diff options
| author | Diego Biurrun <diego@biurrun.de> | 2016-10-13 20:33:15 +0200 |
|---|---|---|
| committer | Diego Biurrun <diego@biurrun.de> | 2017-03-07 08:32:37 +0100 |
| commit | 57b753b445e23363c997a8ec1c556e0b0f6e9da3 (patch) | |
| tree | a3c52e61aa087d38de4346368859424ffd67af74 /doc/optimization.txt | |
| parent | f54037da8af2f2aeb5e5633b48434211e6a97fe5 (diff) | |
build: Prefer NASM assembler over YASM
NASM is more actively maintained and permits generating dependency information
as a sideeffect of assembling, thus cutting build times in half.
Diffstat (limited to 'doc/optimization.txt')
| -rw-r--r-- | doc/optimization.txt | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/doc/optimization.txt b/doc/optimization.txt index be12d85545..3277b9b721 100644 --- a/doc/optimization.txt +++ b/doc/optimization.txt @@ -161,8 +161,8 @@ do{ For x86, mark registers that are clobbered in your asm. This means both general x86 registers (e.g. eax) as well as XMM registers. This last one is particularly important on Win64, where xmm6-15 are callee-save, and not -restoring their contents leads to undefined results. In external asm (e.g. -yasm), you do this by using: +restoring their contents leads to undefined results. In external asm, +you do this by using: cglobal function_name, num_args, num_regs, num_xmm_regs In inline asm, you specify clobbered registers at the end of your asm: __asm__(".." ::: "%eax"). @@ -194,12 +194,12 @@ The latter requires a good optimizing compiler which gcc is not. Inline asm vs. external asm --------------------------- Both inline asm (__asm__("..") in a .c file, handled by a compiler such as gcc) -and external asm (.s or .asm files, handled by an assembler such as yasm/nasm) +and external asm (.s or .asm files, handled by an assembler such as nasm/yasm) are accepted in Libav. Which one to use differs per specific case. - if your code is intended to be inlined in a C function, inline asm is always better, because external asm cannot be inlined -- if your code calls external functions, yasm is always better +- if your code calls external functions, external asm is always better - if your code takes huge and complex structs as function arguments (e.g. MpegEncContext; note that this is not ideal and is discouraged if there are alternatives), then inline asm is always better, because predicting |