0fea54a98
Denys Vlasenko
2025-08-01
Subject
libbb/dump: much faster formatting of %_u on x86
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Commit Diff GitHub →
include/platform.h+1 -1
| @@ -187,7 +187,7 @@ | |
| #elif defined(BYTE_ORDER) && BYTE_ORDER == LITTLE_ENDIAN | |
| # define BB_BIG_ENDIAN 0 | |
| # define BB_LITTLE_ENDIAN 1 | |
| - | #elif defined(__386__) |
| + | #elif defined(__i386__) |
| # define BB_BIG_ENDIAN 0 | |
| # define BB_LITTLE_ENDIAN 1 | |
| #else | |
libbb/dump.c+18 -2
| @@ -494,12 +494,28 @@ static void conv_c(PR *pr, unsigned char *p) | |
| *pr->cchar = 'c'; | |
| printf(pr->fmt, *p); | |
| } else { | |
| - | #if 1 |
| + | #if defined(__i386__) || defined(__x86_64__) |
| + | /* Abuse partial register operations */ |
| + | uint32_t buf; |
| + | unsigned n = *p; |
| + | asm ( //00000000 00000000 00000000 aabbbccc |
| + | "\n shll $10,%%eax" //00000000 000000aa bbbccc00 00000000 |
| + | "\n shrw $5,%%ax" //00000000 000000aa 00000bbb ccc00000 |
| + | "\n shrb $5,%%al" //00000000 000000aa 00000bbb 00000ccc |
| + | "\n shll $8,%%eax" //000000aa 00000bbb 00000ccc 00000000 |
| + | "\n bswapl %%eax" //00000000 00000ccc 00000bbb 000000aa |
| + | "\n addl $0x303030,%%eax" |
| + | "\n" : "=a" (n) |
| + | : "0" (n) |
| + | ); |
| + | buf = n; |
| + | str = (void*)&buf; |
| + | #elif 1 |
| char buf[4]; | |
| /* gcc-8.0.1 needs lots of casts to shut up */ | |
| sprintf(buf, "%03o", (unsigned)(uint8_t)*p); | |
| str = buf; | |
| - | #else // use faster version? +20 bytes of code |
| + | #else // use faster version? +20 bytes of code relative to sprintf() method |
| char buf[4]; | |
| buf[3] = '\0'; | |
| ch = *p; | |