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1 | /* Copyright (C) 2004-2019 Free Software Foundation, Inc. |
---|---|

2 | This file is part of the GNU C Library. |

3 | |

4 | The GNU C Library is free software; you can redistribute it and/or |

5 | modify it under the terms of the GNU Lesser General Public |

6 | License as published by the Free Software Foundation; either |

7 | version 2.1 of the License, or (at your option) any later version. |

8 | |

9 | The GNU C Library is distributed in the hope that it will be useful, |

10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |

11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |

12 | Lesser General Public License for more details. |

13 | |

14 | You should have received a copy of the GNU Lesser General Public |

15 | License along with the GNU C Library. If not, see |

16 | <http://www.gnu.org/licenses/>. */ |

17 | |

18 | #include "div_libc.h" |

19 | |

20 | |

21 | /* 64-bit unsigned long divide. These are not normal C functions. Argument |

22 | registers are t10 and t11, the result goes in t12. Only t12 and AT may be |

23 | clobbered. |

24 | |

25 | Theory of operation here is that we can use the FPU divider for virtually |

26 | all operands that we see: all dividend values between -2**53 and 2**53-1 |

27 | can be computed directly. Note that divisor values need not be checked |

28 | against that range because the rounded fp value will be close enough such |

29 | that the quotient is < 1, which will properly be truncated to zero when we |

30 | convert back to integer. |

31 | |

32 | When the dividend is outside the range for which we can compute exact |

33 | results, we use the fp quotent as an estimate from which we begin refining |

34 | an exact integral value. This reduces the number of iterations in the |

35 | shift-and-subtract loop significantly. |

36 | |

37 | The FPCR save/restore is due to the fact that the EV6 _will_ set FPCR_INE |

38 | for cvttq/c even without /sui being set. It will not, however, properly |

39 | raise the exception, so we don't have to worry about FPCR_INED being clear |

40 | and so dying by SIGFPE. */ |

41 | |

42 | .text |

43 | .align 4 |

44 | .globl __divqu |

45 | .type __divqu, @funcnoplt |

46 | .usepv __divqu, no |

47 | |

48 | cfi_startproc |

49 | cfi_return_column (RA) |

50 | __divqu: |

51 | lda sp, -FRAME(sp) |

52 | cfi_def_cfa_offset (FRAME) |

53 | CALL_MCOUNT |

54 | |

55 | /* Get the fp divide insn issued as quickly as possible. After |

56 | that's done, we have at least 22 cycles until its results are |

57 | ready -- all the time in the world to figure out how we're |

58 | going to use the results. */ |

59 | stt $f0, 0(sp) |

60 | excb |

61 | beq Y, DIVBYZERO |

62 | |

63 | stt $f1, 8(sp) |

64 | stt $f3, 48(sp) |

65 | cfi_rel_offset ($f0, 0) |

66 | cfi_rel_offset ($f1, 8) |

67 | cfi_rel_offset ($f3, 48) |

68 | mf_fpcr $f3 |

69 | |

70 | _ITOFT2 X, $f0, 16, Y, $f1, 24 |

71 | cvtqt $f0, $f0 |

72 | cvtqt $f1, $f1 |

73 | blt X, $x_is_neg |

74 | divt/c $f0, $f1, $f0 |

75 | |

76 | /* Check to see if Y was mis-converted as signed value. */ |

77 | ldt $f1, 8(sp) |

78 | blt Y, $y_is_neg |

79 | |

80 | /* Check to see if X fit in the double as an exact value. */ |

81 | srl X, 53, AT |

82 | bne AT, $x_big |

83 | |

84 | /* If we get here, we're expecting exact results from the division. |

85 | Do nothing else besides convert and clean up. */ |

86 | cvttq/c $f0, $f0 |

87 | excb |

88 | mt_fpcr $f3 |

89 | _FTOIT $f0, RV, 16 |

90 | |

91 | ldt $f0, 0(sp) |

92 | ldt $f3, 48(sp) |

93 | cfi_remember_state |

94 | cfi_restore ($f0) |

95 | cfi_restore ($f1) |

96 | cfi_restore ($f3) |

97 | cfi_def_cfa_offset (0) |

98 | lda sp, FRAME(sp) |

99 | ret $31, (RA), 1 |

100 | |

101 | .align 4 |

102 | cfi_restore_state |

103 | $x_is_neg: |

104 | /* If we get here, X is so big that bit 63 is set, which made the |

105 | conversion come out negative. Fix it up lest we not even get |

106 | a good estimate. */ |

107 | ldah AT, 0x5f80 /* 2**64 as float. */ |

108 | stt $f2, 24(sp) |

109 | cfi_rel_offset ($f2, 24) |

110 | _ITOFS AT, $f2, 16 |

111 | |

112 | .align 4 |

113 | addt $f0, $f2, $f0 |

114 | unop |

115 | divt/c $f0, $f1, $f0 |

116 | unop |

117 | |

118 | /* Ok, we've now the divide issued. Continue with other checks. */ |

119 | ldt $f1, 8(sp) |

120 | unop |

121 | ldt $f2, 24(sp) |

122 | blt Y, $y_is_neg |

123 | cfi_restore ($f1) |

124 | cfi_restore ($f2) |

125 | cfi_remember_state /* for y_is_neg */ |

126 | |

127 | .align 4 |

128 | $x_big: |

129 | /* If we get here, X is large enough that we don't expect exact |

130 | results, and neither X nor Y got mis-translated for the fp |

131 | division. Our task is to take the fp result, figure out how |

132 | far it's off from the correct result and compute a fixup. */ |

133 | stq t0, 16(sp) |

134 | stq t1, 24(sp) |

135 | stq t2, 32(sp) |

136 | stq t3, 40(sp) |

137 | cfi_rel_offset (t0, 16) |

138 | cfi_rel_offset (t1, 24) |

139 | cfi_rel_offset (t2, 32) |

140 | cfi_rel_offset (t3, 40) |

141 | |

142 | #define Q RV /* quotient */ |

143 | #define R t0 /* remainder */ |

144 | #define SY t1 /* scaled Y */ |

145 | #define S t2 /* scalar */ |

146 | #define QY t3 /* Q*Y */ |

147 | |

148 | cvttq/c $f0, $f0 |

149 | _FTOIT $f0, Q, 8 |

150 | mulq Q, Y, QY |

151 | |

152 | .align 4 |

153 | stq t4, 8(sp) |

154 | excb |

155 | ldt $f0, 0(sp) |

156 | mt_fpcr $f3 |

157 | cfi_rel_offset (t4, 8) |

158 | cfi_restore ($f0) |

159 | |

160 | subq QY, X, R |

161 | mov Y, SY |

162 | mov 1, S |

163 | bgt R, $q_high |

164 | |

165 | $q_high_ret: |

166 | subq X, QY, R |

167 | mov Y, SY |

168 | mov 1, S |

169 | bgt R, $q_low |

170 | |

171 | $q_low_ret: |

172 | ldq t4, 8(sp) |

173 | ldq t0, 16(sp) |

174 | ldq t1, 24(sp) |

175 | ldq t2, 32(sp) |

176 | |

177 | ldq t3, 40(sp) |

178 | ldt $f3, 48(sp) |

179 | lda sp, FRAME(sp) |

180 | cfi_remember_state |

181 | cfi_restore (t0) |

182 | cfi_restore (t1) |

183 | cfi_restore (t2) |

184 | cfi_restore (t3) |

185 | cfi_restore (t4) |

186 | cfi_restore ($f3) |

187 | cfi_def_cfa_offset (0) |

188 | ret $31, (RA), 1 |

189 | |

190 | .align 4 |

191 | cfi_restore_state |

192 | /* The quotient that we computed was too large. We need to reduce |

193 | it by S such that Y*S >= R. Obviously the closer we get to the |

194 | correct value the better, but overshooting high is ok, as we'll |

195 | fix that up later. */ |

196 | 0: |

197 | addq SY, SY, SY |

198 | addq S, S, S |

199 | $q_high: |

200 | cmpult SY, R, AT |

201 | bne AT, 0b |

202 | |

203 | subq Q, S, Q |

204 | unop |

205 | subq QY, SY, QY |

206 | br $q_high_ret |

207 | |

208 | .align 4 |

209 | /* The quotient that we computed was too small. Divide Y by the |

210 | current remainder (R) and add that to the existing quotient (Q). |

211 | The expectation, of course, is that R is much smaller than X. */ |

212 | /* Begin with a shift-up loop. Compute S such that Y*S >= R. We |

213 | already have a copy of Y in SY and the value 1 in S. */ |

214 | 0: |

215 | addq SY, SY, SY |

216 | addq S, S, S |

217 | $q_low: |

218 | cmpult SY, R, AT |

219 | bne AT, 0b |

220 | |

221 | /* Shift-down and subtract loop. Each iteration compares our scaled |

222 | Y (SY) with the remainder (R); if SY <= R then X is divisible by |

223 | Y's scalar (S) so add it to the quotient (Q). */ |

224 | 2: addq Q, S, t3 |

225 | srl S, 1, S |

226 | cmpule SY, R, AT |

227 | subq R, SY, t4 |

228 | |

229 | cmovne AT, t3, Q |

230 | cmovne AT, t4, R |

231 | srl SY, 1, SY |

232 | bne S, 2b |

233 | |

234 | br $q_low_ret |

235 | |

236 | .align 4 |

237 | cfi_restore_state |

238 | $y_is_neg: |

239 | /* If we get here, Y is so big that bit 63 is set. The results |

240 | from the divide will be completely wrong. Fortunately, the |

241 | quotient must be either 0 or 1, so just compute it directly. */ |

242 | cmpule Y, X, RV |

243 | excb |

244 | mt_fpcr $f3 |

245 | ldt $f0, 0(sp) |

246 | ldt $f3, 48(sp) |

247 | lda sp, FRAME(sp) |

248 | cfi_restore ($f0) |

249 | cfi_restore ($f3) |

250 | cfi_def_cfa_offset (0) |

251 | ret $31, (RA), 1 |

252 | |

253 | cfi_endproc |

254 | .size __divqu, .-__divqu |

255 | |

256 | DO_DIVBYZERO |

257 |

Warning: That file was not part of the compilation database. It may have many parsing errors.