Mercurial > hg > octave-lojdl > gnulib-hg
comparison lib/vasnprintf.c @ 15959:a18c505b7981
vasnprintf: Optimize bit search operation.
* lib/vasnprintf.c (divide): Use optimizations from integer_length.c.
* m4/vasnprintf.m4 (gl_PREREQ_VASNPRINTF): Require
gl_DOUBLE_EXPONENT_LOCATION.
* modules/vasnprintf (Files): Add m4/exponentd.m4.
* modules/unistdio/u8-vasnprintf (Files): Likewise.
* modules/unistdio/u8-u8-vasnprintf (Files): Likewise.
* modules/unistdio/u16-vasnprintf (Files): Likewise.
* modules/unistdio/u16-u16-vasnprintf (Files): Likewise.
* modules/unistdio/u32-vasnprintf (Files): Likewise.
* modules/unistdio/u32-u32-vasnprintf (Files): Likewise.
* modules/unistdio/ulc-vasnprintf (Files): Likewise.
* m4/isnand.m4 (gl_PREREQ_ISNAND): Use AC_REQUIRE.
| author | Bruno Haible <bruno@clisp.org> |
|---|---|
| date | Sat, 15 Oct 2011 13:20:29 +0200 |
| parents | ed8603738240 |
| children | 8250f2777afc |
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| 15958:ed8603738240 | 15959:a18c505b7981 |
|---|---|
| 551 beta^(m-n-1) <= a/b < beta^(m-n+1). */ | 551 beta^(m-n-1) <= a/b < beta^(m-n+1). */ |
| 552 /* Determine s. */ | 552 /* Determine s. */ |
| 553 size_t s; | 553 size_t s; |
| 554 { | 554 { |
| 555 mp_limb_t msd = b_ptr[b_len - 1]; /* = b[n-1], > 0 */ | 555 mp_limb_t msd = b_ptr[b_len - 1]; /* = b[n-1], > 0 */ |
| 556 s = 31; | 556 /* Determine s = GMP_LIMB_BITS - integer_length (msd). |
| 557 if (msd >= 0x10000) | 557 Code copied from gnulib's integer_length.c. */ |
| 558 # if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) | |
| 559 s = __builtin_clz (msd); | |
| 560 # else | |
| 561 # if defined DBL_EXPBIT0_WORD && defined DBL_EXPBIT0_BIT | |
| 562 if (GMP_LIMB_BITS <= DBL_MANT_BIT) | |
| 558 { | 563 { |
| 559 msd = msd >> 16; | 564 /* Use 'double' operations. |
| 560 s -= 16; | 565 Assumes an IEEE 754 'double' implementation. */ |
| 566 # define DBL_EXP_MASK ((DBL_MAX_EXP - DBL_MIN_EXP) | 7) | |
| 567 # define DBL_EXP_BIAS (DBL_EXP_MASK / 2 - 1) | |
| 568 # define NWORDS \ | |
| 569 ((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) | |
| 570 union { double value; unsigned int word[NWORDS]; } m; | |
| 571 | |
| 572 /* Use a single integer to floating-point conversion. */ | |
| 573 m.value = msd; | |
| 574 | |
| 575 s = GMP_LIMB_BITS | |
| 576 - (((m.word[DBL_EXPBIT0_WORD] >> DBL_EXPBIT0_BIT) & DBL_EXP_MASK) | |
| 577 - DBL_EXP_BIAS); | |
| 561 } | 578 } |
| 562 if (msd >= 0x100) | 579 else |
| 580 # undef NWORDS | |
| 581 # endif | |
| 563 { | 582 { |
| 564 msd = msd >> 8; | 583 s = 31; |
| 565 s -= 8; | 584 if (msd >= 0x10000) |
| 585 { | |
| 586 msd = msd >> 16; | |
| 587 s -= 16; | |
| 588 } | |
| 589 if (msd >= 0x100) | |
| 590 { | |
| 591 msd = msd >> 8; | |
| 592 s -= 8; | |
| 593 } | |
| 594 if (msd >= 0x10) | |
| 595 { | |
| 596 msd = msd >> 4; | |
| 597 s -= 4; | |
| 598 } | |
| 599 if (msd >= 0x4) | |
| 600 { | |
| 601 msd = msd >> 2; | |
| 602 s -= 2; | |
| 603 } | |
| 604 if (msd >= 0x2) | |
| 605 { | |
| 606 msd = msd >> 1; | |
| 607 s -= 1; | |
| 608 } | |
| 566 } | 609 } |
| 567 if (msd >= 0x10) | 610 # endif |
| 568 { | |
| 569 msd = msd >> 4; | |
| 570 s -= 4; | |
| 571 } | |
| 572 if (msd >= 0x4) | |
| 573 { | |
| 574 msd = msd >> 2; | |
| 575 s -= 2; | |
| 576 } | |
| 577 if (msd >= 0x2) | |
| 578 { | |
| 579 msd = msd >> 1; | |
| 580 s -= 1; | |
| 581 } | |
| 582 } | 611 } |
| 583 /* 0 <= s < GMP_LIMB_BITS. | 612 /* 0 <= s < GMP_LIMB_BITS. |
| 584 Copy b, shifting it left by s bits. */ | 613 Copy b, shifting it left by s bits. */ |
| 585 if (s > 0) | 614 if (s > 0) |
| 586 { | 615 { |