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Fix powerpc software sqrtf (bug 17967).
Similarly to sqrt in <https://sourceware.org/ml/libc-alpha/2015-02/msg00353.html>, the powerpc sqrtf implementation for when _ARCH_PPCSQ is not defined also relies on a * b + c being contracted into a fused multiply-add. Although this contraction is not explicitly disabled for e_sqrtf.c, it still seems appropriate to make the file explicit about its requirements by using __builtin_fmaf; this patch does so. Furthermore, it turns out that doing so fixes the observed inaccuracy and missing exceptions (that is, that without explicit __builtin_fmaf usage, it was not being compiled as intended). Tested for powerpc32 (hard float). [BZ #17967] * sysdeps/powerpc/fpu/e_sqrtf.c (__slow_ieee754_sqrtf): Use __builtin_fmaf instead of relying on contraction of a * b + c.
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@ -1,3 +1,9 @@
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2015-02-13 Joseph Myers <joseph@codesourcery.com>
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[BZ #17967]
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* sysdeps/powerpc/fpu/e_sqrtf.c (__slow_ieee754_sqrtf): Use
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__builtin_fmaf instead of relying on contraction of a * b + c.
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2015-02-12 J William Piggott <elseifthen@gmx.com>
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[BZ #17969]
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2
NEWS
2
NEWS
@ -10,7 +10,7 @@ Version 2.22
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* The following bugs are resolved with this release:
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4719, 15467, 15790, 16560, 17912, 17932, 17944, 17949, 17964, 17965,
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17969.
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17967, 17969.
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Version 2.21
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@ -87,26 +87,28 @@ __slow_ieee754_sqrtf (float x)
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/* Here we have three Newton-Raphson iterations each of a
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division and a square root and the remainder of the
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argument reduction, all interleaved. */
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sd = -(sg * sg - sx);
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sd = -__builtin_fmaf (sg, sg, -sx);
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fsgi = (xi + 0x40000000) >> 1 & 0x7f800000;
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sy2 = sy + sy;
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sg = sy * sd + sg; /* 16-bit approximation to sqrt(sx). */
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e = -(sy * sg - almost_half);
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sg = __builtin_fmaf (sy, sd, sg); /* 16-bit approximation to
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sqrt(sx). */
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e = -__builtin_fmaf (sy, sg, -almost_half);
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SET_FLOAT_WORD (fsg, fsgi);
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sd = -(sg * sg - sx);
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sy = sy + e * sy2;
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sd = -__builtin_fmaf (sg, sg, -sx);
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sy = __builtin_fmaf (e, sy2, sy);
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if ((xi & 0x7f800000) == 0)
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goto denorm;
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shx = sx * fsg;
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sg = sg + sy * sd; /* 32-bit approximation to sqrt(sx),
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but perhaps rounded incorrectly. */
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sg = __builtin_fmaf (sy, sd, sg); /* 32-bit approximation to
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sqrt(sx), but perhaps
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rounded incorrectly. */
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sy2 = sy + sy;
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g = sg * fsg;
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e = -(sy * sg - almost_half);
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d = -(g * sg - shx);
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sy = sy + e * sy2;
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e = -__builtin_fmaf (sy, sg, -almost_half);
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d = -__builtin_fmaf (g, sg, -shx);
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sy = __builtin_fmaf (e, sy2, sy);
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fesetenv_register (fe);
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return g + sy * d;
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return __builtin_fmaf (sy, d, g);
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denorm:
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/* For denormalised numbers, we normalise, calculate the
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square root, and return an adjusted result. */
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